1) Which is the topic sentence? ________________We take air in through our nose or mouth. The air we breathe enters our lungs, where oxygen enters our blood. Then we breathe out carbon dioxide. This system keeps our body supplied with oxygen. a) The respiratory system is important b) The respiratory system helps us breathe. c) The respiratory system has lungs 2) Which is the topic sentence?________________. The heart pumps blood every second. Blood carries oxygen and nutrients to all our organs. It also takes away waste. This system keeps everything in the body working. a) The circulatory system is important b) The heart is part of the circulatory system c) The circulatory system moves blood around the body. 3) Which is the topic sentence? _________________The brain sends messages through the nerves. These messages help us move, think, and feel. The nervous system also keeps us safe by reacting quickly. It is the communication system of our body. a) The nervous system controls everything we do. b) The brain controls your thoughts c) Your body has different organs that help you survive 4) Which is the topic sentence? _________________ Our muscles work with our bones when we walk, run, or jump. They also help us smile, blink, and chew. Some muscles even work without us thinking, like the heart. Muscles give our body strength and movement. a) The muscular system helps our body move. b) The muscles are important c) You can't move without muscles

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