(While) copper, (unlike gold) , ( is not considered) a glamorous metal, it (has long been) one of the world’s valuable commodities.

The answer is E (No error). Why is the error not A? shouldn’t it be although? Why is it allowed to be while?

After (servicing every vehicle in the fleet), the alarming grinding noises that had been coming from many of the trucks disappeared.

(a) servicing every vehicle in the fleet
(b) servicing all the vehicles in the fleet
(c) every vehicle in the fleet has been serviced
(d) all the vehicles in the fleet had been serviced
(e) servicing all the fleet’s vehicles

What is the answer, and why? Thank you!