Here are the comparative sentences based on the information provided:

1. The average rainfall in Arica, Chile is less than the average rainfall in the Libyan Sahara Desert, which is more than 15 mm per year. (dry)
- **The average rainfall in Arica, Chile is drier than the average rainfall in the Libyan Sahara Desert.**

2. I arrived early at the meeting at 7 o’clock; I arrived at 6:45. (soon)
- **I arrived sooner than Henry, who arrived at the meeting at 7 o’clock.**

3. It costs 100 million dong to build a concrete bridge, but only 50 million dong to build a steel bridge. (expensive)
- **Building a concrete bridge is more expensive than building a steel bridge.**

4. It takes Linh 45 minutes to load hay onto the cart, but his father needs only 30 minutes. (slowly)
- **Linh loads hay onto the cart more slowly than his father does.**

5. His house’s yard is about 100 square meters while your house’s yard is about 50 square meters. (large)
- **His house’s yard is larger than your house’s yard.**

6. It was very difficult to travel to the town 5 years ago. Now people can drive a car or take a bus to the town. (easily)
- **People can travel to the town more easily now than they could 5 years ago.**

7. I do yoga three times a week, but my sister does it almost every day. (frequently)
- **My sister does yoga more frequently than I do.**

8. The Australian athlete jumped 8.78m. The American athlete jumped 8.59m. (far)
- **The Australian athlete jumped farther than the American athlete.**

9. The Mekong River is 4.350 km long, while the Red River is 1.149 km long. (long)
- **The Mekong River is longer than the Red River.**

10. A horse can run 80 km/h while a dog can run 50 km/h. (fast)
- **A horse runs faster than a dog.**