A、  B、  C、  A(A)不知道对方何时回到镇上的陈述句同时也包含了询问对方何时回来的意思。所以该项回答昨天回来为正确答案。(B)重复使用in town这一表达方式，易造成误导。(C)使用同音异义词back，易造成误导。

When will the shipment arrive?
(A)For shipping and handling.
(B)Not before next Monday.
(C)The conference will be in May.

I didn’t know you were back in town.
(A)I got back yesterday.
(B)I just stayed in town.
(C)Yes, I have serious problems with my back.