Choose the best option A, B, C or D to complete the passage from 1 to 6

V. Choose the best option A, B, C or D to complete the passage from 1 to 6
Scientists have known a lot (1) _____ the Earth. They understand how mountains (2) _____ made and what a volcano is. The following example is about volcanic eruptions. Mt. Vesuvius in Italy and Mt. Helens in the USA are both (3 ) _____ mountains. They are both volcanoes. A volcano is a mountain that is open at the top. Smoke and hot air come out of the hole. Sometimes very hot rock comes out of the mountain. That can (4) _____ trouble for people nearby. This is what happened with Mt. Vesuvius and Mt Helens. Hot rock poured out of Mt. Vesuvius and (5) _____ the town of Pompeii in 79 A. D. Everyone in the town was killed. The Mt. Helens volcano didn’t kill many people. There were no cities closed to the mountain. But the hot rock killed a large part of the forest. And a lot of dirt fell on cities many miles away. Today there are still many questions for scientists (6) _____ study the earth. They do not know when a volcano will send hot rock intothe air. They still are not sure about the inside of the earth.
1. A. about B. to C. for D. of
2. A. is B. are C. was D. were
3. A. excellent B. good C. famous D. beautiful
4. A. make B. be made C. making D. been made
5. A. cover B. covering C. covered D. to cover