It's six o'clock now, it's time ________.

[　　]

Tell Lin Tao to ring me up if he ________ back.

[　　]

--What shall we do this Sunday?

--Why ________ to the Science Museum?

[　　]

The school trip________ be pleasant, if it were sunny today.

[　　]

In the street I met the scientist ________ gave us a talk last week.

[　　]

We'll climb Xiangshan Hill if it ________ tomorrow.

[　　]

We can't come into the teachers' office ________ permission.

[　　]

Lucy writes as ________ as Lily. They are both good students.

[　　]

I don't know ________ to play this new game.

[　　]

I can't think ________ any good ideas to give her.

[　　]