How does a warm front form?

a. warm air becomes caught between cold air masses.
b. two air masses meet and stay separated.
c. warm air moves over cold air and replaces it.
d. cold air moves under warm air and pushes it up.

Impressions of tropical swamp plants were observed on rocks in polar regions. the impressions were dark black imprints, which means the fossils are examples of ( 1 ) the fossils tell us that polar regions ( 2 ) ( 1 ) a. carbonization b. mineralization c. trace fossils ( 2 ) a. had tropical plants that can grow in ice b. might have had a diffierent climate in the past c. will have abundent vegitation