下 英语同义句

题目

下 英语同义句
It's necessary for them to support and help each other both before and during the event.(改为同义句)
------ ------ and ------ each other ------ ------- for them both brfore and during the event.
麻烦解释一下是用is还是are啦

答案

( To support ) and ( help ) each other( is necessary ) for them both brfore and during the event.
分析：不定式,动名词等作主语时谓语动词用单数.
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