Topic: Sequence of Tense,

Best Answer Explained in Below-:

The phrase "It is high time" is typically followed by a verb in the subjunctive mood, which expresses a suggestion or recommendation about something that should occur. In this context, the correct verb form to follow "It is high time" is in the past tense, even though the action is expected to take place in the present or future.

In the given options, "encouraged" (Option A) is the past tense form of the verb "encourage." This aligns perfectly with the construction “It is high time we all encouraged students to study science,” implying that the action should start happening now, reflecting a sense of urgency about the need to promote science education among students.

On the other hand, the other options do not fit grammatically in this context: "encourage" (Option B) is present tense, "encouraging" (Option C) is a gerund or participle, and "to encourage" (Option D) is an infinitive form. None of these correctly conveys the subjunctive mood required by "It is high time." Therefore, "encouraged" is the only option that maintains proper grammatical structure and intent.