Here are the correct answers based on the traffic signs:

1. **D. No parking allowed.** (The sign indicates no parking)
2. **C. You must go straight.** (The sign usually means you can’t go left or right)
3. **D. Trucks can go here.** (The sign indicates no entry for trucks)
4. **B. You mustn’t go straight ahead.** (The sign indicates the road is closed ahead)

Feel free to ask if you need further explanations!