—Shall we go for a picnic in the forest park tomorrow?
—Yes, ________ it rains heavily.
A.if B.unless C.until D.when
—Shall we go for a picnic in the forest park tomorrow?
—Yes, ________ it rains heavily.
A.if B.unless C.until D.when
B unless引导条件状语从句,表示“除非”,符合语境。故选B。