In the given question, a part of a sentence is printed in bold. Below each sentence, some phrases are given which can substitute the bold part of the sentence. Find out the phrase which can correctly substitute that part of the sentence. If the sentence is correct as it is, mark the answer as 'No correction required' or 'No Improvement'.
The reason why he wrote the letter was because he could not contact him by email.
for which he wrote the letter was because
The reason he wrote the letter was that he could not contact him by email.