【C7】A．remainB．keepC．makeD．cause

【C15】A．remainB．keepC．makeD．cause

Cooling makes the engine metals their mechanical properties.A.RemainB.to remainC.retainD.t

【C7】A．resultB．reasonC．causeD．phenomenon

【C7】A．makingB．madeC．to makeD．make

【C7】A．reasonB．purposeC．causeD．goal

【C7】A．variationsB．consequencesC．effectsD．causes