챕터16 명사절

14번

Ms. Kang was not sure ______ briefcase was left in the conference room after the seminar.

답은 (d)whose 인데요 (c)why는 왜 안되나요?

20번

Mr. Lee has to arrive at the convention center ____ 4 o'clock to set up the company's exhibition booth.

(b)until

(c)by

p153에 by와 until이 전치사 역할을 하면서 ~까지 뜻을 가지고 있다고 나오는데

왜 (b)는 오답이고 (c)만 정답인가요?