先化简,再求值:x+3(2y+x),其中x=﹣2,y=1.
解:原式=x+6y+3x
=4x+6y;
当x=﹣2,y=1时,
原式=4×(﹣2)+6×1
=﹣2.
The children remembered to ______ themselves at first, but things went out of control minutes later.
A.produce
B.behave
C.practice
D.enjoy
在生理状态下呼吸中枢的兴奋性依赖于()
A.血浆H+浓度
B.低浓度的CO2
C.高O2浓度
D.正常的CO2浓度
E.迷走神经的传入冲动