There is no doubt _____ China has made rapid progress in space exploration.
| A． whether | B． that | C． which | D． who |
--- I rang you at about ten, but there was no reply.
--- Oh, that was probably ____ I was seeing the doctor.
| A．when | B．why | C．what | D．that |
15. _______ all the inventions have in common is _____they have succeeded.
A. What; what B. That; that C. What; that D That; what
This old computer must have been of great use to _______ did the scientific research.
| A．those | B．when | C．whoever | D．whomever |
--- Do you know _____ Mr. Black’s address is.
--- He may live at No. 18 or No. 19 of Bridge Street. I'm not sure of _____.
| A．what; which | B．where; which | C．where ; what | D．what; where |
--- Do you know him?
--- Yes, but I can’t remember ________I met him for the first time.
A. where B. what C that D. if