Cubes of boiled egg white are put into test-tubes that contain $5\ \text{cm}^3$ of water. Boiled egg white has protein. As shown in the table, different additional substances are put into each test-tube. After the test-tubes have been left for eight hours, they are then checked for amino acids. Which test-tubes indicate that pepsin is an enzyme?
- A1 and 4
- B2 and 7
- C4 and 5
- D5 and 6