Mark the letter A, B, C or D on your answer sheet to indicate the underlined part that needs correction in each of the following questions.

The main rotor and tail rotor of(A)  a helicopter make(B) the same(C) job as the wings(D) , propellers, and rubber of an airplane.

Up to now_________,space  exploring still remains_________very  risky, complex, and expensive endeavor.

The higher one rises in the atmosphere_________, the temperature generally becomes.

Mark the letter A, B, C or D on your answer sheet to indicate the underlined part that needs correction in each of the following questions.

The wave lengths(A)  of ultraviolet light are shorter than that (B) of visible light but (C) longer than those (D) of X-rays.

The workers decided to_________ until their demands were met.

It was not until she arrived at school_________realized she had forgotten her book.

Allan: “Do you mind if I use your dictionary?”             Nick: “ _________.”

With the help of modern devices, those who suffer hearing or vision                  find life easier.