He decided________ Public Administration.

Infinitive:
- An infinitive is the word “to” + a verb’s root.

- নির্দিষ্ট কিছু এর ক্ষেত্রে, বিশেষ করে verbs of thinking and feeling এর পর to-infinitive ব্যবহৃত হয়। যেমন: To walk is a good exercise.

- এরকম কিছু verb হলো: Choose, decide, forget, expect, hope, hate, intend, learn, like, love, mean, plan, prefer, remember, want, would like/love etc.
Example: They decided to spend a holiday together.

- Some verbs are followed by a direct object and then the to-infinitive: for example:

Example: He encouraged his friends to vote for him.

10 Common verbs following by infinitives:
Like, want, hope, agree, plan, decide, choose, promise, need

Source: British Council Learning website & engvid.com