Maps differ from photographs in many different ways, including:
a. lack of cultural bias in maps
b. showing "invisible" aspects such as political boundaries
c. complete accuracy in maps
d. always showing good weather

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.