In the following sentence supply a verb in agreement with its subject:
Ninety rupees _______ too much for this bag.
a) is
b) are
c) were
d) be

Hint: We are asked to check the subject-verb agreement here. This, therefore, demands us to look at how the subject and verb agree in number.

Complete answer:
Knowing the subject-verb agreement helps us understand the basic structuring of a sentence. This agreement or concord registers how a word changes its singular-plural form depending on the other words or tense related to it.
According to the agreement, the verb following a singular noun should always be plural and that following a plural noun should be singular. The same is applicable vice-versa too.
That being the case, we understand that the subject or noun in the given sentence is ‘ninety rupees’ which is plural in the count. Therefore, we identify that the verb following this will be ‘is’ and not ‘are’.
Option (a) has ‘is’ in it and hence, option a is the right answer.
Option (b) is wrong as ‘are’ is the plural form of ‘is.’ This cannot go with the plural subject and so it's incorrect here.
Similarly, ‘were’ in option (c) is the past tense of ‘are’ and clearly cannot suit the given sentence.
Option (d) is also wrong. Though ‘be’ is a form of is, are, and were; it cannot be the right choice here.
Hence option (a) is correct.