11. The new camera didn't work, so Minh took it back to the shop. (A. so/back)
12. We cannot swim in this part of the river because the water is highly polluted. (A. because)
13. I'm tired because I stayed up late watching TV. (C. when)
14. She wants to go home because she feels sick. (B. because)
15. There will be big floods if you cut down the trees. (C. if)
16. Baths use twice as much water as showers. However, I suggest taking a shower. (B. however)