Q: Fact 1: Plasma cells are activated B cells that secrete antibodies. Fact 2: Antibodies are protein molecules. Given the two facts above, plasma cells are activated B cells that secrete what?

Available choices: 1). heat or cold 2). harmful substances 3). Leptospirosis 4). bioaerosols 5). protein molecules 6). Chemical energy 7). major threat to health 8). Veins and arteries.
The answer is:
5).