Identify which of the following sentences has a compound subject.
A. While the Puerto Rican flag is red, white, and blue, the design is different from that of the US flag.
B. Each country has its own distinctive flag, with different colors and designs.
C. Among all the state flags in the United States, California's flag is the only one with a bear pictured on it.
D. Red, white, and blue are the colors of the Puerto Rican flag.
