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

[Q]: Passage: Relative dating determines which of two fossils is older or younger than the other but not their age in years. Relative dating is based on the positions of fossils in rock layers. Lower rock layers were laid down earlier, so they are assumed to contain older fossils. This is illustrated in Figure below . Answer: relative
[A]: What type of dating determines which of two fossils is older or younger than the other but not their age in years?

[Q]: Passage: By losing an electron, the sodium atom becomes a sodium ion. It now has one less electron than protons, giving it a charge of +1. Positive ions such as sodium are given the same name as the element. The chemical symbol has a plus sign to distinguish the ion from an atom of the element. The symbol for a sodium ion is Na + . Answer: becomes sodium ion
[A]: What happens when a sodium atom loses an electron?

[Q]: Passage: The cardiovascular system transports many substances to and from cells throughout the body. Answer: cardiovascular
[A]:
What system transports many substances to and from cells throughout the body?