Question

the main human activity that releases greenhouse gases is texting on cellphones burning fossil fuels eating meat using bottled water

Explanation:

Burning fossil - fuels such as coal, oil, and gas releases large amounts of carbon - dioxide ($CO_2$), which is the most prevalent greenhouse gas shown in the pie - chart (79.7%). Other activities have much smaller greenhouse - gas footprints compared to burning fossil fuels.

Answer:

burning fossil fuels