Which substance in cigarettes is a thick, brownish sludge containing carcinogens?

The energy needs of a human population are not affected by

Suggest why placing wheels under a heavy box reduces the neccessary force required to push it along at a constant speed.

The ancestors of plants that lived in water had plenty of water for the young. angiosperms are a group of land plants that evolved a reproductive trait for living on land. this trait protect young plants by allowing them to grow only when water is present and the conditions for healthy development are right. what trait most likely young angiosperms in this way?