题干
By the time my mum got home, I _______ my homework.
A：have finished
B：had finished
C：finished
D：will finish
答案(点此获取答案解析）
B
By the time my mum got home, I _______ my homework.
A：have finished
B：had finished
C：finished
D：will finish
R+2M中，已知R和M的相对分子质量之比为22:9.当1.6g