His parents with their friends_____(plant)500 trees this month alone
问题描述：
His parents with their friends_____(plant)500 trees this month alone
答
His parents with their friends__have planted___(plant)500 trees this month alone
仅这个月这种了500棵树.强调种的结果.这个月还没过去,可以用现在完成时.是用has还是have是have，因为parents是主语，是复数。with their friends不是主语的组成部分，可以把它放到句子的后面。