Serious threat to our ecology and environment can be .............. with organic cultivation.
1). hastened
2). impeded
3). aggravated
4). combated
combated (Verb) : stopped something unpleasant or harmful from happening or from
getting worse
hastened (Verb) : to make something happen sooner or more quickly
impeded (Verb) : delayed or stopped the progress of something
aggravated (Verb) : made an unpleasant situation worse
Here, combated is the right usage.