Can someone tell me which one to click?

The biggest component / ingredient of summer time smog is

What’s the reason for not digging up aztec ruins in modern mexico city

The controlled use of fire by hominids: (a) limited the expansion of hominids into certain environments, such as dry grasslands. (b) decreased the amount of food energy available in the hominid diet. (c) contributed to geographical expansion and food production techniques in positive ways. (d) has been shown to contribute little to the digestive process of hominids.