Explanation:

Correct answer is (c). If we read the two sentences, we can observe that they are related by cause and effect relationship. And among the choices available, only ‘because’ can be used in this context since it means ‘the reasons thereof’. Combing the two sentences the complete sentence will be: It is time that the Environment ministry does away with all kinds of illegal mining activities in the country because the irreparable damage caused by these activities is going to contribute a lot to the global warming.
Option C is the right choice.