题干
— Where's Lucy ? — She ________ in the office. I saw her there just now.
A：can't be
B：must be
C：can be
D：should be
答案(点此获取答案解析）
B
— Where's Lucy ? — She ________ in the office. I saw her there just now.
A：can't be
B：must be
C：can be
D：should be
b ，则实数
的值为