下列昆虫中，不具备多型现象的是（）
A.褐飞虱
B.棉蚜
C.玉米螟
D.白背飞虱
参考答案：C
John overslept this morning. Otherwise he wouldn’t have been late for school. ( ) The logical relationship between the above sentences is______.
A．additive
B．adversative
C．causal
D．temporal
