Question

—         have you stayed in Shanghai?
— For about seven days.
A. How soon                   B. How long           C. How often

Answer 1

B

根據答語For about seven days.大約七天了，可推斷出上句問的是“你在上海呆了多長時間了？所以選B，How soon 多久，How often 表示頻率，多久一次。