Answer:
5. Fifteen kilometers <em><u>is</u></em> a nice distance to ski in an afternoon.
6. Analyzing sentences for grammatical purposes <em><u>is</u></em> even better than watching paint dry.
7. Economics <em><u>is</u></em> almost as fascinating as accounting.
Explanation:
The use of "is" or "are" depends majorly on the condition of the noun involved. This means that if the noun is singular, we use "is" while for plural nouns, we use "are".
In the given sentences, "is" and "are" are used as follows-
5. In this sentence, the distance "fifteen kilometers" is taken as a single unit even though the word "kilometers" is in the plural state. Thus, the helping verb will be "is".
6. Here, the verb "analyzing" is taken as a gerund, thereby functioning as a noun. And so, the helping verb used will be "is".
7. Similarly, this sentence contains the noun "economics" which is a branch of study and thereby taken as a singular noun. Thus, the verb will be "is".
Thus, in all three sentences, the helping verb used will be "is".
