造成黄土高原千沟万壑地表形态的根本原因是（ ）
看图，读一读，选择正确的句子。
A. Hello. This is my mother. I loveher.
B. Hello. I'm Grandma and this is yourGrandpa.
C. Look, this is my classmate. His nameis Bob.
D. Good morning, Kitty.
