Answer: B. Is
Explanation: The sentence is referring to the present moment, so the appropriate verb form is "is." The sentence should read: "It is convenient, let's go out for a drink tonight."
Here’s why the other options are not suitable for the sentence:
A. Be: "Be" is an infinitive form and does not fit grammatically in this context. The sentence requires a finite verb that indicates the present tense.
C. Was: "Was" is the past tense of "is" and would be appropriate if the sentence referred to a past situation. However, since the sentence talks about the present (going out tonight), "was" is incorrect.
D. Were: "Were" is the past tense plural form of "to be" and is used for hypothetical or conditional situations (e.g., "If it were convenient..."). It does not fit the present tense or the context of making a straightforward statement about current convenience.