Have you sent thank-you notes to the relatives from _ _ you received gifts?

题目

Have you sent thank-you notes to the relatives from _ _ you received gifts?
Have you sent thank-you notes to the relatives from _ _ you received gifts?
为什么不填that ,填whom

答案

因为这里需要指代的是 relatives,亲戚们
from 是要和 receive 连在一起理解