Using half normal saline or hypotonic solution is appropriate in patients who are dehydrated. Hypotonic solutions have less osmotic pressure making it absorbable attracting more water thus it makes intracellular volume of cells increased, which leads to patient's safe hydration.
The answer is the first one. It is the most realistic out of the four answers.
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a, because exercise doesn't just aid the prevention of certain diseases, it helps prevent many diseases. i would've chosen d if it wasn't so specific but a is the correct answer.