The sunspot came into its active stage, __________ that happens once every eleven years.
A．one B．it C．the one D．what
It’s already 10’clock. I wonder how it ____ that she was two hours late on such a short trip.
A．came over B．came out C．came about D．came up
Many strange new means of transport have been developed in our century, the strangest of _____ being perhaps the hovercraft(气垫船).
A．which B．them C．that D．it
___ the temperature might drop, coal was prepared for warming.
A．To consider B．Considered C．Considering D．To be considered
We had a really bad time about six months ago but now things are ____.
A．looking up B．coming up C．making up D．turning up
--- The research on the new bird flu virus vaccine is challenging and demanding. Who do you think can do the job?
---____ my students have a try?
A．Shall B．Must C．Will D．May
