Monday is the first day . . . . . . . the week. A. of B. after C. during D. before

The correct answer is A. of.

Monday is the first day of the week. It is followed by Tuesday, Wednesday, Thursday, Friday, Saturday, and Sunday.

The other options are incorrect because:

• After
  Subscribe

  Join Our Telegram Channel

  on YouTube
  Monday is Tuesday.
• During Monday is not a meaningful phrase.
• Before Monday is Sunday.