283.___ crops will be produced next year is not yet decided.
a.it b. what c. that d. which为什么选C，我觉得都行？详细解释 各答案翻译?


284.90% of the debts ___ so far.
a.is paid back b. have been paid off c.has been paid off d. are paid off为什么选C，不是Ｂ？我觉得都行？详细解释 各答案

283.___ crops will be produced next year is not yet decided.
a.it b. what c. that d. which为什么选C，我觉得都行？详细解释 各答案翻译?
答：本句前面是主语从句，引导主语从句连词有that,whether,who,what,whatever等，不能由which来引导，it是代词，更不能引导，所以答案a与d是错的。what 相当于 the thing that,所以如果用what，则一定要在从句充当主语或者宾语，如：What caused the accident remains unknown（what作主语），What we need is time（what作宾语）.
可这个句子中的从句中既有主语，且是被动语态，不需要宾语，所以不能用what.
综上所述，只能选C，也就是that
284.90% of the debts ___ so far.
a.is paid back b. have been paid off c.has been paid off d. are paid off为什么选C，不是Ｂ？我觉得都行？详细解释 各答案
答：答案a时态不对，句子显然是完成时。还款与还债只能是pay back或pay off(两意思稍有区别，前者是偿还，后者是偿清)，不能用pay of，所以答案d也是错的。
表示金钱，时间，价格或度量衡的名词，虽然看来是复数，但通常看作一个整体，谓语一般用单数。例如：
Three weeks was allowed for making the necessary preparations. 用三个星期来做准备。
Ten yuan is enough. 十元够了。
所以选b也不妥。
综上所述，只能选选C