18. 下列何種機械在操作時，有可能發生後拋現象？ (A)帶鋸機(B)圓鋸機 (C)鑽孔機(D)線鋸機。

5. If an aircraft is operating at 40,000 ft. the pressurization ensures that (A)sea level pressure is maintained in the cabin. (B)the cabin pressure is progressively increased until the operational height is reached. (C)the cabin pressure above 10,000 ft. (D)the cabin pressure is equivalent to an altitude of less than 10,000 ft.