求下列函数f（x)的f'-（0)及f'+（0)，又f'（0)是否存在：

Dennis ,if you are late again, I’ll phone your parents .I’m(),you know.

A.serious

B.careful

C.true

D.promising

A、A. to stay, do

B、B. stay, do

C、C. to stay, to do

D、D. stay, to do

A.without they permitting

B.although they says other

C.no matter what they says

D.despite their saying it

—How do you visit your parents？

—About three times a year.

-- How often do you go to see your parents？-- ______.

A．In no time

B．After a while

C．In a short time

D．From time to time

A:(). B:She works in the Oxford University.

A. What does your mother do？

B. What do your parents do？

C. What are your parents doing at the moment？

—How do you visit your parents？

--About three times a year.

A.much

B.long

C.often

— ______ do you write to your parents？— Twice a month.

A．How long

B．How soon

C．How often