.So often ______ in recent years that it has almost become a rule.
| A．has this happened | B．this has happened |
| C．is this happening | D．for this to happen |
My friend Mary is _____ beautiful girl and _____ girl everyone likes to work with.
| A．a, a | B．a, the | C．the, a | D．the, the |
She may have missed the train, in _____ case she won't arrive for another hour.
| A．whose | B．that | C．which | D．what |
Many countries, for example, Mexico and Japan, _____a lot of earthquakes.
| A．have | B．having | C．to have | D．having had |
Mother told Jim to watch the milk until it boiled and then _____ off the gas.
| A．turn | B．turning | C．turned | D．having turned |
Your mother, however, ____ say that to us that day.
| A．does | B．did | C．is doing | D．was doing |