Select the most appropriate option to fill in the blank.

Your explanation was simpler ______ Rekha’s explanation.

than

The correct option to fill in the blank is than.

The sentence is comparing your explanation to Rekha's explanation, and the word "than" is used to compare two things. In this case, you are saying that your explanation was simpler than Rekha's explanation.

The other options are incorrect.

• Of is used to indicate possession or belonging. For example, "The explanation of the problem is on the whiteboard."
• That is used to refer to something that has been mentioned before. For example, "I understand that explanation."
• Then is used to indicate a sequence of events. For example, "I explained the problem, and then Rekha explained it again."