After several hours of futile research, Karim decided to then take a break before he would resume his search for pertinent data once again.
The infinitive verb “to take” should not be split by the word “then.” If you wanted to keep the "then" in the sentence but not split the infinitive, you might place it after "Karim" and before "decided."
940 MCQ for effective preparation of the test of Verb and Tenses of English Grammar section.
Read the MCQ statement: After several hours of futile research, Karim decided to then take a break before he would resume his search for pertinent data once again., keenly and apply the method you have learn through the video lessons for Verb and Tenses to give the answer. Record your answer and check its correct answer and video explanation for MCQ No. 118-4397.