Methyltetrachloride (MTC) is chemical found in some

Premise: Methyltetrachloride (MTC) is chemical found in some pesticides, glues, and sealants.
Premise: Exposure to MTC can cause people to develop asthma.

Conclusion: In order to halve the nation's asthma rate, the government has announced that it will ban all products containing MTC.

MTC………………cause asthma………………ban MTC………………….to halve asthma rate

This conclusion indicates that MTC is ONE OF THE MAJOR CAUSES OF ASTHMA and not any other cause is present. Therefore, it assumes that by banning MTC, asthma rate would go down by half.

Let’s look at the choices:
(A) Exposure to MTC is responsible for no less than half of the nation's asthma cases.
This is the correct choice.
Negated statement: Exposure to MTC is responsible for LESS THAN HALF of the nation’s asthma rate. Then MTC does not contribute much to the asthma rate. There are some other reasons for this. It matches our pre-thinking.

(B) Products containing MTC are not necessary to the prosperity of the American economy.
Prosperity of the American economy is OUT OF SCOPE here because it is not the concern for the government at the moment.

(C) Asthma has reached epidemic proportions.
OK but how does banning MTC helps. INCORRECT.

(D) Exercise and proper nutrition are helpful in maintaining respiratory health.
OUT OF SCOPE. No information on MTC……

(E) Dust mites and pet dander cause asthma.
Irrelevant because it does not tell that is this contribution more than MTC’s or not………