We’ll put off the outing until next week, ____________ we won’t

We’ll put off the outing until next week, ____________ we won’t be so busy.
A、when
B、which
C、what
D、as
【正确答案】：A
【题目解析】：非限制性定语从句；先行词为next time，关系词指代next time 在从句中做时间状语，因此选A when