A. After taking inflation into account, a new deluxe automobile costs only slightly more than a new model did in 1970.
Cost is not mentioned in the argument. We are taking about durability and number of vehicles on road. This one is out of scope.

B. The number of automobiles built by deluxe each year has not increased sharply since 1970
Suppose the company build 1,000 units each year till 2005(70,000 - Total) ,then 10,000 units each year till 2012(total 70,000) and the life of vehicle is only 5 years, then we can say the argument is invalid, as the evidence is deceiving(number of vehicles on road will be half of the vehicles manufactured since 1970). By saying that the number of units have not sharply increased, we can eliminate this possibility. So this is the correct option.

C. Owners of deluxe automobiles typically keep their cars well maintained
So deluxe automobile got lucky. This doesn't undermine the evidence.

D. Since 1970, Deluxe has made few changes in the automobiles it manufactures than other car companies have made in their automobiles.
The argument is about durability. If they are still using same parts and the consumer is accepting, still there argument and evidence holds true.

E. Deluxe automobiles have been selling at relatively stable prices in recent years.
Again, out of scope.