One protective measure to prevent asphyxiation is that the gas is

The correct answer is that the gas should be odorized, so that one can smell it.

Explanation:

The condition in which the body gets severely deficient to oxygen due to abnormal breathing is termed as asphyxiation. This can be a result of various factors, however, the prime cause due to which it happens in the workplace is because of the accidental leakage of some kinds of gases or chemicals used in the region that the workers are not familiar with. Thus, one of the safeguarding measures, in order to prevent asphyxiation, is that the gas should be odorized so that one can smell it.

the answer to your question is:

c. complementary base-pairing

b.