_____ is even important _____ as the earth cooled down, water began to appear on its surface.
| A．That, which | B．What, that |
| C．What, what | D．It, that |
After three hours'climbing，they reached ________ they thought was the place they'd been dreaming of.
| A．what | B．which | C．where | D．that |
Engines are to machines ________ hearts are to animals.
| A．as | B．that | C．what | D．which |
The last time we had great fun was ________ we were visiting the Water Park.
| A．where | B．how | C．when | D．why |
—I prefer shutting myself in and listening to music all day on Sundays.
—That's ________ I don't agree.You should have a more active life.
| A．where | B．how | C．when | D．what |
Part of the reason Charles Dickens loved his own novel，David Copperfield，was ________ it was rather closely modeled on his own life.(2010·北京)
| A．what | B．that | C．why | D．whether |