Improve the highlighted part of the sentence.
The snowstorm will effect thousand of travellers.

Correct option is B

The correct substitution of the highlighted words is (b) affect thousands.
" Effect" is a noun, but we need a verb — " affect" means to influence or cause change (Hindi: असर डालना). Also, " thousand" should be in plural form i.e., " thousands" to match the general quantity.
Grammatical rule used: Use of verb vs. noun – "affect" is a verb, "effect" is usually a noun.
Example: Pollution may affect the health of people.
 Information Booster: "Effect" is used as a verb only in formal contexts meaning “to bring about”, which doesn’t fit here.