按照Chailakhyan的成花素假说，冬萝卜在短日照条件下不能成花，是由于缺少（）的缘故。
参考答案：GA
---Do you know ________?
--- I'm not sure. Maybe he is a businessman.
A． who he is
B．who is he
C．what he does
D．what does he do
