If everyone ______ here, let’s begin our school trip.[ ]
A.am
B. is
C. are
D. do
答案:B
Out of the crowded bus ______, who was dressed in a black suit, waving to a woman.
A.a tall man stepped
B.stepped a tall man
C.did a tall man step
D.a tall man did step
下图为人体内细胞与内环境之间的物质交换示意图,请据图回答:
若C为肌细胞,长时间剧烈运动后,血浆成分发生一些变化,图示中()(填A或B)端乳酸含量会增加,但血浆pH依旧会保持稳定,此时参与稳态调节的主要物质是()等。