There are $m$ books in black cover and $n$ books in blue cover, and all books are different. The number of ways these $\left(m+n\right)$ books can be arranged on a shelf so that all the book in black cover are put side by side is

• A

  $m!n!$
• Correct answer
  B

  $m!\left(n+1\right)!$
• C

  $\left(n+1\right)!$
• D

  $\left(m+n\right)!$

Hence, the correct answer is option: 'B'.