A:has to be put off
B:must have been put off
C:has to put off
D:must put off
梧州的苍海湖蓄水以后对沿岸气温能起一定的调节作用,这主要是因为水的( )
设函数f(x)定义在R上,它的图象关于直线x=1对称,且当x≥1时,f(x)=3x﹣1,则有( )