請問一下 EARN 的問法問題

He helps his Dad and Mom _____________money (兩個答案).
1.earns
2.earn
3.earning
4.earn

怎麼2與4重複？4應該是to earn吧？

本題空格可填三種：
He helps his Dad and Mom earn money.
He helps his Dad and Mom to earn money.
He helps his Dad and Mom earning money.

第一、二句helps是準使役動詞(不完全全及物動詞），其受詞補語可用原V或to V，意思是幫忙去賺錢，還沒賺錢。

第三句helps是完全及物動詞，分詞片語是修飾性質，意思是爸媽在賺錢中，去幫幫忙。

He helps his (Dad and Mom) earn money.
=Dad and Mom as a plural subject use a plural verb

He helps his Dad and Mom (earning) money.
=earning is a gerund consisting of a gerund and its accompanying words, used as a noun:-(earning money);
=eg:-He helped his parents to (earning money.)= a gerund.