瞬时速度
参考答案:
是时均流速和脉动速度的代数和
— Has Sam finished his homework today?
— I have no idea. He ________ it this morning.
A.did
B.was doing
C.has done
D.had done
犬产后低血钙症的典型症状是()。
A.腹泻
B.排尿困难
C.肌肉痉挛
D.血红蛋白尿
E.呼吸困难