just want to know ------ I should set off right now.A.when B.where C.whether D.that

选C
句意：我想知道我是否应该现在出发.
whether引导宾语从句,作know的宾语.
set off 出发,动身
句中已有right now,即“现在”,说明时间很明确,无需when
where需要地点
that引导宾从需要“确定内容”,从I want to know可以看出不确定