1、So precious is time that we can't afford to waste it.
时间是如此珍贵，我们不能浪费它。
2、The reason why we have to grow trees is that they can supplyfresh air for us.
我们必须种树的原因是它们能供应我们新鲜的空气。
共有16种时态，分别是：
1. 一般现在时 simple present tense
2. 现在进行时 present progressive tense
3. 现在完成时 present perfect tense
4. 现在完成进行时 present perfect progressive tense
5. 一般过去时 simple past tense
6. 过去完成时 past perfect tense
7. 过去将来时 past future tense
8. 过去进行时 past progressive tense
9. 一般将来时 simple future tense
10. 将来进行时 future progressive tense
11. 将来完成时 future perfect tense
12.将来完成进行时 future perfect continuous tense
13.过去完成进行时 past perfect continuous tense
14.过去将来进行时 past future continuous tense
15.过去将来完成时 past future perfect tense
16.过去将来完成进行时 past future perfect continuous tense。