Are you looking (1)………………………a cheap, clean, effective source of power that doesn’t (2)…………………………pollution or waste natural resource? Look no further than solar energy. While most fuels now in use are (3)………………………burned at a big rate, solar energy, a power from the (4)………………………, will last as long as the world (5)……………………….This energy has been (6)……………………..to heat and cool homes or to cook food. It has been used (7)…………………… radio batteries and provided power for telephone lines. The devices, (8)…………………….., are cheap to operate but very expensive to produce.
Điền vào số 6
A. waste
B. used
C. not used yet
D. use
Đáp án B