选出最恰当的答案( )
A:To visit China.
B:To try something new.
C:To make friends.
D:To learn something easy.
已知曲线y=2ax2+1经过点a,3,则曲线在该点处的切线方程是 ( )
读图回答。
一般卧室里不能摆放过多的植物过夜,这是因为( )