介词在小作文中的价值可见一斑，准确使用介词对于取得至关重要，因此在准备知识里诸老师重点给出三个常用介词的使用方法，这三个介词经常用于动态数据描写，分别是to, by, of。在使用的时候，我们要注意by是跟在动词后面，表示的是幅度，而of是跟在名词后面，同样表示幅度，to则既可以跟在动词也可以跟在名词之后，表示的是最终的数值大小。下面我们来看几个例子：
1). This year unemployment has increased by 20,000 cases.
2). This year there has been an increase in unemployment of 5%.
3). This year unemployment has risen to 10%.
4). This year there has been a rise in unemployment to 10%.
不论是静态还是动态数据，我们在描述中经常会发现某2个数据间存在倍数关系，或者某一个数据在经过增长后和前面一个时间点的数据存在倍数关系，这时候，从的角度来说，我们需要对于这些倍数作适当的描述。表示倍数关系的单词主要有以下这些：double / triple / quadruple（2/3/4倍）, fold, times等。前面三个动词可以直接在句子中表达具体的倍数，一般用于静态数据的描写；而后面两个单词需要借助名词词组的形式来表达倍数，一般用于动态数据：
1). In general, the number of global population rose sharply during the six centuries and climbed to around six billion in 2000, a growth of 12 times.
2). Around 80% of the graduates from college C are able to find employment within six months after graduation. This figure triples that of college A while college B has 50%.
3). Minors constituted nearly 30% of the population in Utah. This figure doubles that of California while Florida had 21%.
我们注意一下个句子中的名词短语，其中文意思为增长了12倍，我们可以用a 12-folded growth对其进行替换，效果是一样的，但是中文意思发生了细微的变化，为一个12倍的增长。在第二和第三个句子中，划线的动词都是及物动词，直接可以将倍数关系表达出来，其使用的句子结构大家也不妨仔细体会一下。
1). On average, 11% of all households, comprising almost two million people, were in this position.
2). 300 employees attend full-time course, constituting almost one third of all the employees.
3). Next comes tree-cutting, taking away slightly larger areas of land than farming in all the three regions.
4). Observing the overall workforce does not lead to any surprises as it simply combines the above two, with about two-thirds of all workers working full-time or long hours, and the remaining one-third working part-time.
1). However, those consisting of only one parent or a single adult had almost double this proportion of poor people, with 21% and 19% respectively.
2). Couples generally tended to be better off, with lower poverty levels for couples without children (7%) than those with children (12%).
3). By contrast, the annual distance covered by bicycle, motorbike and air travel only represented an insignificant share, with less than 8 billion passenger kilometers for each.
4). Role play and education games had less successful sales, with 7% each.
5). In comparison, student expenditure in country C was considerably lower, at only US $1,500 per year.
6). Observing the overall workforce does not lead to any surprises as it simply combines the above two, with about two-thirds of all workers working full-time or long hours, and the remaining one-third working part-time.
1). In the first stage, the used bottles, discarded by customers, are collected at the collecting point.
2). Following this, the clean bottles are transported by the trucks to the glass factory where they are broken into glass pieces which are put into a furnace
3). In the final stage, new and empty bottles are filled with liquid, packed and dispatched to the supermarket ready to be picked by consumers.
4). Nitrogen is poured in. Water is needed only when it is hot in weather.
1). The year 1860 saw a doubling in the number of homes, but the size of farmland and woods was reduced by half.
2). In the same year, a bridge could be seen over the river and a road was constructed linking the river to the residences.
3). Several school buildings and sports facilities were constructed at the south-eastern corner of the village, which were connected with the residential area in the north by a newly-built road.
1). The number of world population rose slowly in the first 400 years from 1400. However, this was suddenly replaced by a sharply upward trend after 1800 and the figure surged to over 6 billion in 2000.
2). In the first 20 years, the amount of oil discovered increased dramatically by 50%. However, from 1990 onwards, it was suddenly replaced by a sharply downward trend and is predicted to dip to only 20,000 barrels in 2020.
3). From Monday to Friday, the dinner sales rose gradually by 20%. However, it was suddenly replaced by a downward trend when the weekend set in, dipping quickly by 10%.
4). This rise in passenger kilometer number was recorded in air, bus an rail travel but a slight decline was actually found in bicycle and motorbike travel.
5). This upward trend is expected to last through to the year 2021, when the population is estimated at 87,657,000, more than double the 1901 figure.
1). The rest of the students’ spending was divided among leisure, books and others.
2). Leisure spending constituted a larger percentage(20%) of student expenditure in both country A and country B, while in country C more money was spent on books(21%) than on leisure(12%).