Answer:
D
Explanation:
have/has/had been (v.) is one of the structure of passive voice
Answer:
The correct answer would be C. hope this helps!
Explanation:
The primary problem is the greenhouse effect. Greenhouse effect is when some gases (including CO2) absorbs some portion of sun's heat to make the atmosphere warm to support life. But when the amount of CO2 etc. increases in the atmosphere, it heats up more than it is required. So, by limiting CO2 emission, we can solve this problem.
