─ ________ bad weather! It makes me down.
─ Yes. _________ rainy morning!
A:What; What
B:What a; What
C:What a; What a
D:What; What a
如图所示,已知F是以O为圆心,BC为直径的半圆上任一点,A是弧BF的中点,AD⊥BC于点D,求证:AD= 12 BF.
家养的动物与同种的野生动物相比(如家猪和野猪),往往会发生较大的变异,请解释其原因。