The Mississippi River which is over 2300 miles long is the second-longest river in the United States. (单选题)
A.
The Mississippi River which is over 2300 miles long is the second-longest river in the United States. (No commas)
B.
The Mississippi River, which is over 2300 miles long is the second-longest river in the United States.
C.
The Mississippi River which is over 2300 miles long, is the second-longest river in the United States.
D.
The Mississippi River, which is over 2300 miles long, is the second-longest river in the United States.