The number of acres destroyed by wildfires, which have become an ongoing threat due to drought and booming population density, have increased dramatically over the past several years, prompting major concern among local politicians.

a)have become an ongoing threat due to drought and booming population density, have increased
b)have become an ongoing threat due to drought and booming population density, have been increasing
c)has become an ongoing threat because of drought and booming population density, has increased
d)have become an ongoing threat due to drought and booming population density, has increased
e)have become an ongoing threat because of drought and booming population density, has increased