_______environmental damage is done, it takes many years for the ecosystem to recover．
| A．Even if | B．If only | C．While | D．Once |
______ you call me to say you’re not coming, I’ll keep waiting for you at the theatre.
| A．Unless | B．When | C．If | D．As |
A chair made of steel is stronger, though costs much more, than _____ made of wood.
| A．that | B．one | C．it | D．those |
In autumn, it’s beautiful outside with golden fallen leaves _______ the ground.
| A．covering | B．to cover | C．having covered | D．covered |
I’d appreciate _____ if you would like to teach me how to use the computer.
| A．that | B．it | C．this | D．you |
Always read the ______ on the bottle carefully and take the right amount of medicine.
| A．explanations | B．instructions | C．descriptions | D．introductions |