Mexico city, mexico, and san salvador, el salvador, are both a. located on islands b. located near active volcanoes c. at risk for hurricane flooding, as both are near the coast d. located on the rio grande

The answer is: B. located near active volcanoes 
The group of active volcanoes that located in these regions is referred to as The Central America Volcanic Arc.
Some of these volcanoes such as The Izalco mountain,erupted almost continuously from late 1700s until mid-1900s.

Ithink d would be correct