Given a scientific passage and an answer, generate a question for the given answer.

Passage: The first period of the Paleozoic Era was the Cambrian. By the beginning of the Paleozoic, organisms evolved shells. Shells could hold their soft tissues together. Shells could protect them from predators and from drying out. Some organisms evolved external skeletons. These are called exoskeletons . Organisms with hard parts also make good fossils. Fossils from the Cambrian are much more abundant than fossils from the Precambrian. Answer: cambrian
The first period of the paleozoic era was called what?

Passage: Transcription takes place in three steps: initiation, elongation, and termination. The steps are illustrated in Figure below . Answer: transcription
Initiation, elongation, and termination are the three steps of what?

Passage: All living things need energy. They need it to power the processes of life. For example, it takes energy to grow. It also takes energy to produce offspring. In fact, it takes energy just to stay alive. Remember that energy can't be created or destroyed. It can only change form. Energy changes form as it moves through ecosystems. Answer: form
Energy cannot be created or destroyed - it can only change what?