whoever
填whoever还是whomever主要是看从句,所填词语在从句中做主语就是whoever,做宾语就是whomever.
判断所做成分必须要把主句和从句分开并都还原为正常语序,该句分开并还原后应为：
I'll give this book to him\her.
He\She wants to have it.
这样就很明显能看出所填成分做主语,所以填whoever