Fill in the blanks with the most appropriate option:-

I should be glad if you ……. come in the evening.

would

The correct option to fill in the blanks is would.

The sentence is about the speaker's polite request for the listener to come in the evening. The modal verb "would" is used to express politeness or a wish. It is the most appropriate modal verb to use in this context, as it describes the speaker's desire for the listener to come in the evening.

The other options are not as appropriate:

• Could is also used to express politeness, but it is not as strong as "would".
• Will is used to express certainty or determination. It is not as appropriate as "would", as it does not convey the same sense of politeness or deference.
• Should is used to express obligation or duty. It is not as appropriate as "would", as it does not convey the same sense of politeness or desire.