Studies documenting the arrival of spring and fall in the Northern Hemisphere are based on: A. average daily temperatures as measured at locations throughout Northern Hemisphere. B. fixed calendar dates that have been consistent for the past 150 years. C. when buds of particular plants open and when the leaves of particular plants change color and fall. D. average snow melt, precipitation, and consistently increasing or decreasing temperatures across the state. E. the amount of pollution, particularly greenhouse gases, found in the atmosphere of that region.

Option C              

Explanation:

Spring throughout the Northern Hemisphere coincides with that of the March solstice, that may occurs on March 19, 20, as well as 21. (The March equinox signals the beginning of winter throughout the Southern Hemisphere, whereas the September solstice marks the beginning of early fall).

The vernal equinox happened on March 20 and sometimes 21 for much of the last generation. Although, this year the solstice occurs across all U.S. time frames on just the 19th, rendering it the soonest fall we'll saw in our life (so far). The very last occasion this autumn came was in 1896 – a record 124 years earlier!