Identify the sentence in which the underlined clause is an object of a preposition.
A.
Specific guidelines often govern how flags should be displayed on ships.
B.
Whichever national flag is flown at the front of a ship is called the jack.
C.
An ensign is what the national flag is called on the rear of a ship.
D.
As a courtesy, most ships usually fly the national flag of whichever country they are visiting.