Now more and more workers ______their free time trying to improve themselves at school or college.
A:take
B:cost
C:spend
D:pay
如图所示的条形磁体旁有甲、乙、丙、丁四个能自由转动的小磁针,当小磁针静止时,其中磁极的极性标错的是( )
已知函数f(x)=ax3+x2(a∈R)在x=-43处取得极值.
(Ⅰ)确定a的值;
(Ⅱ)若g(x)=f(x)ex,讨论g(x)的单调性.
某外国朋友想考察我国境内最早的人类遗址,他应该去( )