A:Happy birthday to you
B:Let me help you with your English
C:Please remember me to your grandparent
D:Don’t forget to post the letter
下面关于图中四条河流水文特征的叙述,正确的是( )
若多项式 (x+1)(x−3) = x2+ax+b ,则a,b的值分别是( )
生物进化的直接证据是( )