— The computer is working all the time.
— Sorry. I have forgotten ______.
A:turn it off
B:to turn it off
C:turning it off
D:turned it off
图中的玻璃罐模拟池塘生态系统.请回答(1)﹣(4)题.
Daniel is ____ in our class.
12−18 =____
16+13 =____