67. Investigators agreed that passengers on the airliner ______ at the very moment of the crash.

　　A) should have died B) must be dying

　　C) must have died D) ought to die

　　68. The energy ______ by the chain reaction is transformed into heat.

　　A) transferred B) released

　　C) delivered D) conveyed

　　69. ______ their work will give us a much better feel for the wide differences between the two schools of thought.

　　A) To have reviewed B) Having reviewed

　　C) Reviewing D) Being reviewed

　　70. During the process, great care has to be taken to protect the ______ silk from damage.

　　A) sensitive B) tender

　　C) delicate D) sensible