Answer: (1) Inhales (breathes in) Oxygen - good for the body - gives it to the Circulatory System to be transported throughout the body through the blood. (1) Digestive System gets nutrients (good) from food and hands it over to the blood and Circulatory System then carries those nutrients where they need to go.
Answer:
Three hydrogen atoms to form PH₃.
Explanation:
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In this case, since the elements belonging to the nitrogen family (N, P, As, Sb and Bi) show five valence electrons, because there are five electrons at their outer shell, it is clear that if phosphorous bonds with hydrogen, it is going to require the same amount of oxygen atoms (3) because elements having five valence electrons need 3 bonds in order to attain the octet (5+3=8).
Therefore the compound would be:

Which is phosphine.
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A. LITTORAL ZONE is a freshwater ecosystem that is home to rooted plants.
Littoral zone is the shallow area of a lake, pond, river or ocean. This is the area where mangroves grow.
Some counties and water district identify littoral zones so that these zone will be planted with native plants. This is done for the purpose of having the plants purify the water and maintain a balanced ecosystems.
This is an observational study, because the researcher is simply observing the answers of the survey without influencing the outcome in any way. Another example of an observational study would be if a researcher was trying to determine the effects that eating strictly organic foods has on overall health.