同义句改写【小题1】To plant trees every year is necessary for us. for us to plant trees every year.

问题补充：

同义句改写

【小题1】To plant trees every year is necessary for us.

for us to plant trees every year.

【小题2】Paul left Canada two days ago.

Paul Canada since two days ago.It is necessary

答案：

(答案→)It is necessary

解析：

【小题1】考查固定句型。不定式可以作主语，it is necessary to do sth做某事很有必要，故填It is necessary。

【小题2】考查时态。ago与过去时连用，since+含有过去时的句子，与现在完成时连用。leave是短暂动词，不能与一段时间连用，应该转换为be away，故填has been away from。