— Have you decided ______ with her?
— ______.
A:go; Certainly
B:to go; Not yet
C:going; Have already
D:to go; No yet
已知函数fx=-x3+ax2-x-1在-∞,+∞上是单调函数,则实数a的取值范围是( )
小希在学习了密度和浮力的相关知识后,利用自制的量筒和其他实验器材按照如图所示的步骤进行了实验.请结合图提供的信息,计算:
有了光,自然界才绚丽多彩.下列有关光的说法中不正确的是( )
— ______ do you usually do at weekends, Susan?— I usually help my parents do some housework.