The fact has worried many scientists the earth is becoming warmer and warmer these years.
| A．what | B．which | C．th at |
D．though |
Many students today suffer from ________ problems, since they are under too much pressure.
| A．recreation-related | B．pollution-related |
| C．stress-related | D．pollution-free |
________ energy is generated from natural resources—such as sunlight, wind, rain, tides and so on.
| A．Recyclable | B．Non-renewable |
| C．Rechargeable | D．Renewable |
Effective measures have been taken to prevent _______pollution.
| A．exhausted gas | B．exhausting gas |
| C．exhaust gas | D．exhaustion gas |
It worried her a bit ____ her hair was turning grey.
| A．while | B．that | C．if | D．for |
_______you come or not is up to you.
| A．What | B．If | C．Why | D．Whether |