工业上采用的蒸发热源通常为（）。
A、电炉
B、燃烧炉
C、水蒸气
D、太阳能
参考答案：C
Don’t start reading a book ________ you find that it’s one you can read with ease and understanding.
A．when
B．if
C．unless
D．though
Would you mind me how English words?
A. tell; to remember B. telling; remember C. telling; to remember
