(Question)
Answer the following question given this paragraph: Of course, calcium is critical for many other biological processes. It is a second messenger in many signaling pathways, and is essential for muscle contraction, nerve impulse transmission, and blood clotting. Given these roles, it is not surprising that blood calcium levels are tightly regulated by the endocrine system. The organs involved in the regulation are the parathyroid glands. Q: Blood calcium levels are tightly regulated by the what system? Choices: - digestive - cardiovascular - nervous - endocrine A:
(Answer)
endocrine

(Question)
Answer the following question given this paragraph: 42.1 Circulatory systems link exchange surfaces with cells throughout the body. Q: What organ systems link exchange surfaces with cells throughout the body? Choices: - vascular - pulmonary - nervous - circulatory A:
(Answer)
circulatory

(Question)
Answer the following question given this paragraph: Look at this rusty bike. It has been left outside in damp weather too many times, so the iron in the metal parts has rusted. Iron rusts when it combines with oxygen in the air. Iron rusting is an example of a chemical reaction. In a chemical reaction, substances change into entirely different substances. For example, the iron in the bike and the oxygen in the air have changed into rust. Q: A rusty bike has been left outside in damp weather too many times, so the iron in the metal parts have? Choices: - melted - eroded - decayed - rusted A:
(Answer)
rusted