Question

blooms in death valley
in march 2016, death valley national park in california experienced a rare occurrence: thousands of yellow wildflowers covered the region in a \super bloom.\ why was this unusual? death valley is the hottest and driest place in north america. the areas average yearly precipitation is just two inches, making it a challenging place for flowers to grow. however, in october 2015, the valley had received more than three inches of rain in some areas. as a result of the unusually wet season, wildflower seeds that had been lying dormant underground suddenly began to grow, producing an abundance of golden blooms.
what is the main, or central, idea of the passage?
because of the hot, dry conditions in death valley, it is difficult for flowers to grow there.
because of an unusual amount of rain, thousands of wildflowers grew in death valley in 2016.

Explanation:

The passage first introduces that in March 2016, Death Valley had a "super bloom" of yellow wildflowers. Then it explains that Death Valley is usually hot and dry (average yearly precipitation is just two inches, challenging for flowers). But in October 2015, there was an unusually wet season (more than three inches of rain in some areas), which made dormant wildflower seeds grow. So the main idea is about the reason (unusual rain) for the wildflower growth (thousands of wildflowers) in 2016.

Answer:

Because of an unusual amount of rain, thousands of wildflowers grew in Death Valley in 2016.