Select the correct indirect form of the given sentence.
"You must work hard to succeed in your new venture", said the mother to her son.

A

The mother ordered her son to work hard to succeed in his new venture.

B

The mother requested her son to work hard to succeed in his new venture.

C

The mother pleaded her son to work hard to succeed in his new venture.

D

The mother advised her son to work hard to succeed in his new venture. .