Which is a leading theory for the formation of fossil fuels?

a. fossil fuels arrived on earth from comets and asteroids.

b. carbon dioxide levels decreased, resulting in nitrogen fixation.

c. earth cooled, changing oxygen into carbon.

d. fossil fuels are the remnants of organisms that lived a long time
ago and were buried, heated, and formed into hydrocarbons.

What is the farthest destination to date for a human spaceflight mission?

Refer to this portion of a dichotomous key for fish identification to answer the question. 1. (a) has a single dorsal fin ® 5 (b) has a double dorsal fin ® 2 2. (a) one fin is spiny, the other is smooth ® 3 (b) one fin is not spiny or smooth ® 4 5. (a) has small fin on back near tail ® 6 (b) has no fin on back near tail ® 7 6. (a) has barbs near the mouth ® catfish (b) does not have barbs near the mouth ® 10 7. (a) tail is asymmetrical ® 8 (b) tail is symmetrical ® 9 10. (a) scales are small ® trout (b) scales are large ® whitefish what is the next step to complete to identify a fish that has a single dorsal fin, no fin on the back near the tail, and no barbs near the mouth? step 2 step 5 step 7 step 10

What is the membrane that sheath of schwann cell containing cytoplasm and nucleus that encloses myelin