ㅠㅠ[what/that] I like to do most is to spend time outdoors.

여기서 what이 선행사를포함한주격관계대명사이라서답인건알겠는데 that은 왜안되나요?.?

또 the reason why he said so is that he thought to have been deceived by her
여기서 thought뒤에 to 가 왜들어가나요?.?

앗ㅠㅠ하나더있어요 문장구조분석좀해주세요ㅠㅠ
Soil in which there are many fibrous roots is protected from erosion