Here are the completions for the sentences:

1. **What is the price of a dish of five-coloured sticky rice?**
**How much is a dish of five-coloured sticky rice?**

2. **Why did some ethnic peoples build the communal house?**
**What was the reason some ethnic peoples built the communal house?**

3. **How long have you been an engineer?**
**When did you start being an engineer?**

4. **Who do these beautiful cottages belong to?**
**Whose are these beautiful cottages?**

5. **What is the distance between your house and the boarding school?**
**How far is it from your house to the boarding school?**

6. **What is the number of students in your class?**
**How many students are there in your class?**

7. **Would you mind carrying my basket for me, please?**
**Could you carry my basket for me, please?**

8. **What was the reason for him to take part in the voluntary activities?**
**Why did he take part in the voluntary activities?**