In statement given below, a part of the sentence is enclosed in quotation marks. Below are given alternatives to the quotes part which may improve the sentence. Choose the correct alternative. In case no improvement is needed, option 'D' is the answer.The reason "why he wrote the letter was because" he could not contact him over the phone.

• A. why he wrote the letter was since
• B. for which he wrote the letter because
• C. why he wrote the letter was that
• D. No improvement