Answer:
The correct answer is- a. They do not impair thinking.
Step-by-step explanation:
Histamine is the chemical that is involved in an inflammatory and allergic response in the body. It is a neurotransmitter and also regulates immune response in the body.
Antihistamine is the drugs that block the symptoms of allergy by blocking the histamine by binding on histamine receptor. There are two generation histamine 1st generation and 2nd generation.
The first-generation histamine has a central effect which means it affects CNS but second-generation histamine can not easily cross the blood-brain barrier so its capacity to adversely affect CNS is low therefore they do not impair thinking. So the right answer is a.