2문제 질문요~~

안녕하세요~

13. only after he had acquired considerable facility in speaking, he began to learn to read and write.

왜 네번째 밑줄 부분이 틀린건지 잘모르겠어요~

15. it was her who represented her country in the united nations and later became an ambassador to the united states.

왜 두번째 밑줄이 틀린거죠?