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1·It is necessary that we weigh the pros and cons of including English words in Chinese dictionaries.

权衡在汉语词典中加入英语单词的利弊，这对我们来说是很有必要的。

2·To compare the compositions of a meteorite and the Sun, it is necessary that we use ratios of elements rather than simply the abundances of atoms.

为了比较陨石和太阳的成分，我们需要利用元素的比率，而不单单是原子的丰度。

3·It is necessary that a critic develop a sensibility informed by familiarity with the history of art and aesthetic theory.

批评家必须在熟悉艺术史和美学理论的基础上培养一种感性。

4·It is necessary that we help the disabled.

我们很有必要帮助残疾人。

5·It is necessary that everyone be there in time.

大家都按时到达那里是必要的。

6·It is necessary that we buy Christmas gifts now.

我们有必要现在就买圣诞礼物。

7·It is necessary that food be sent to them at once.

有必要把食物立即给他们送去。

8·It is necessary that he read English aloud every day.

你们每天大声读英语是很有必要的。

9·It is necessary that you train yourself before the walk.

在步行前你锻练自己是很有必要的。

10·It is necessary that we should clean the room every day.

我们每天打扫房间，这是必需的。