The more safety restrictions the government puts on

unless there is a trap, No choice other than D came close for me

D is correct
I went for B assuming higher cost was because of manufacturers adding in extra features - obv an incorrect assumption!

I think this one is a real stinker. I agree that D is probably the right answer.

Although this is worded as an inference question, the stimulus (the paragraph) clearly provides a flawed argument, with a conclusion, evidence, and some missing assumptions. The vast majority of inference questions simply provide evidence in the stimulus, and ask you to choose the answer choice which is a logically sound conclusion based on the evidence. This one belongs to a rare and more difficult type.

In this rare type of inference question, what you must find is a NECESSARY assumption. The question asks for something that MUST be true if the statements in the paragraph are true. As noted already, the paragraph contains evidence and a conclusion which doesn't follow from that evidence. If that conclusion is nevertheless TRUE (as the question says), then any necessary assumptions must also be true. If those assumptions weren't true, then the conclusion would not be true.

The conclusion is that overall automobile costs will go up if the government introduces a new restriction. The evidence is that cars become safer if the government adds restrictions, and that safer cars can be sold at a higher price. For overall automobile costs to go up, these safer cars must actually BE sold, which is what choice D provides.

Choice B looks attractive as well, but it appears to be unnecessary. The evidence states that cars DO become safer if the government institutes restrictions, so B more or less restates this piece of evidence.

A question might arise because the conclusion refers to new safety features IN GENERAL, using side air bags as an example, while choice D (and A and B) refer specifically to side air bags. This still works: The conclusion makes a claim about ALL new safety features, and so if it is true, it must apply to ANY new safety feature -- such as side air bags.

one more D.

Nice explanation...
I marked B at the begining..... but it was wrong

(A) If more car manufacturers add side air bags to their cars, some people will buy old cars to save money. - INCORRECT There is no information given saying that old cars will save money, hence out of scope
(B) Some car manufacturers will add additional safety features if the side air bags are required. - INCORRECT - irrelevant or non-existant relationship is given
(C) More people will avoid buying new cars, if car prices increase. - INCORRECT - there is no information given regarding the relationship of car prices and preference of buying cars
(D) If the side-impact air bag restriction is instituted, more people will buy cars. CORRECT - restatement of the conclusion that safer the car, more preferred it becomes
(E) If the only restrictions on cars were those that apply to other products, more companies would manufacture cars. - INCORRECT - no information about other products is given in the passage

Nice question!...Spent more than a couple of minutes looking for a trap --- D wins...

tricky one ... IMO D