Select the most appropriate option to improve the bold part of the sentence.
He insisted to go home.

Correct option is D

The correct substitution of the highlighted words is (d) on going.
Explanation: The verb insist collocates with the preposition on/upon followed by a gerund (V+ing): insist on/upon doing something. Hence, “He insisted on going home.” Another correct frame is “insist that + subject + base verb (subjunctive)” → “He insisted that he go home.”
Grammatical rule used:
· Verb + preposition + gerund: certain verbs (insist on, succeed in, look forward to, etc.) take a preposition and then a gerund, not an infinitive.
· Mandative subjunctive with “insist (that)”: insist that + subject + base form (no -s).
· Example: “They insisted on meeting the manager.” / “They insisted that the manager meet them.”
· Information booster: With insist, both on/upon + V-ing and that + bare infinitive are standard; to + infinitive after “insist” is non-standard.
Why other options are incorrect:
· (a) going on (preposition order wrong) → should be on going after “insisted.”
· (b) upon going is grammatically possible ( insisted upon going), but the most common collocation is on going; the test’s key expects (d).
· (c) that he goes uses the indicative; for mandative use, standard is that he go (subjunctive).