关于情态动词的两道题if you don't like to swim ,you _____ stay at home

if you don't like to swim ,you _____ stay at home .
A.should as well B.may as well C.can as well D.would as well
答案是B,may/might as well do sth 是固定搭配"还是.好,不放.(做某事)"的意思.
He began to write two hours ago.He _______ have finished the article now .
A.must B.ought C.ought to D.had to
答案是C.因为他说He began to write two hours ago.所以猜测他可能/应当已经finished the article now .并不能确定他肯定是完成了那个文章的.所以不能用must,因为must是对事实非常确定的意思.

我觉得，先抛开题不说，可以先想想你一般说话时（中文）怎么说。
第一个，一般来讲，大家讲话时都会说“如果你不想去游泳，你也可以在家待着”。不会说“如果你不想去游泳，你也能在家待着”。can一般是强调能否做一件事情， 例如you can do something/ you cant do something, because it is very dangerous.
第二个，同样道理...

if you don't like to swim , you _____ stay at home .
A. should as well B. may as well C. can as well D. would as well
答案是B, 但我觉得C也可以,那为什么不选C呢 ??
may as well 意思是"也可以",语气上比"can as well(也能...

may的语气更委婉
must相当于肯定的意思，ought to 不确定的成分更多一些