Here are the completed sentences with the correct tense of the verbs:

1. My friend asked me what I **can** do to keep the campsite clean.
2. Mandy asked me if the boys **were reading** the book at present.
3. The teacher told us that we **would travel** to the Mekong River the following month.
4. They say that they **have never traveled** to Scotland before.
5. Jason and Victoria told me they **were working** on a project on environmental protection then.
6. I wondered why Nick **was going** to Ba Vi National Park every summer.
7. John wondered whether he **might be able** to cycle in the Dolomites.
8. She asked me if everyone **had to** ask for permission before entering Son Doong Cave.
9. My mom said she **was** going to visit a friend of hers in London.
10. Shannon said that she **needed** to train every day for her trekking trip.
11. The guests wanted to know what time the jeep tour **was starting**.
12. They all wondered what they **had to do** to restore damaged ecosystems.