| Investigators concluded that human failure was not responsible for the fatal airplane crash last August，and since that time new and more stringent rules for identifying and reporting me chanical problems have been in effect.That accounts for the fact that reports of airplane mechanical problems have increased in frequency by 50 percent since last August.
Which one of the following is an assumption underlying the argumentin the passage?
(A)Airplane traveli s still relatively safe，despite the increase in reported mechanical problems.
(B)Mechanical problems in airplanes have increased dramatically since last August.
(C)Mechanical problems in airplanes have not increased by 50 percent since last August.
(D)Airlinesarel essreluctant to report mechanical problems than they previously were.
(E)Mechanical problems in airplanes have be come easier to detectsince last August.