What causes clouds of dust and gas to form a protostar?
(1) magnetism (3) expansion of matter
(2) gravitational attraction (4) cosmic background radiation

Which of these is a drawback of using natural gas? a. it is fairly safe for use in homes.b. it burns more cleanly than crude oil products.c. scientists have developed new ways of extracting it.d. during its extraction, groundwater can be contaminated.