—You were out when I dropped in at your house.
—Oh, I ________ for a friend from England at the airport.
| A．was waiting | B．had waited | C．am waiting | D．has waited |
When you go outing with your sisters, you must see to ________ that they are safe.
| A．everything | B．it | C．them | D．yourself |
A model or an experiment in a science class can help students see things which would ______ remain hidden.
| A．otherwise | B．still |
| C．thus | D．therefore |
Written in a hurry, ________. How can it be satisfactory?
| A．they found many mistakes in the report |
| B．Sam made lots of mistakes in the report |
| C．there are plenty of mistakes in the report |
| D．the report is full of mistakes |
Is ________48 hours________ the man- made satellite ________ is made in our country to orbit the planet around?
| A．it; that; where | B．it; when; what |
| C．it for; that it takes; that | D．it; that it takes; which |
Use your head! Nothing taught by others can have the same effect on you as ________learned by yourself．
| A．those | B．what | C．that | D．the one |