identify the different places on a map

What was the great rift valley formed by

Sink holes may eventually for to join a. wide valleys b. zone of aeration c. dripstones d. aquifer

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.