Topic: Conditional Sentence,

Best Answer Explained in Below-:

The sentence "It would be pleasant if we - where to go" is an example of a counterfactual conditional statement, often expressed in the subjunctive mood in English. The subjunctive mood is used to discuss hypothetical situations or wishes that are not based on reality. In this context, the phrase suggests imagining an ideal scenario.

Among the options provided, "knew" (Option C) is the correct choice. This form is the simple past tense of the verb "know" and is typically used in subjunctive constructions to convey a situation that is contrary to fact. The structure of the sentence implies a wish or an unreal condition: the speaker is contemplating the pleasantness of a situation if they had knowledge about where to go.

In contrast, the other options fail to fit the grammatical structure or meaning required:
- "had known" (A) is a past perfect tense, which doesn’t align here since the sentence calls for a simple past subjunctive form.
- "known" (B) is the past participle form, which is not appropriate in this conditional context.
- "knower" (D) is not a verb and does not grammatically fit into the sentence structure at all.

Thus, "knew" (C) not only aligns with the meaning intended but also adheres to the correct use of the subjunctive mood in English.