C & D are only part of the question and unsuitable, so it's either A or B, but I'd say it's more likely A~<span> How does changing the amount of water affect the growth of corn? </span>
The correct answer is: A. How does changing the amount of water affect the growth of corn?
While options B, C & D are not impossible to test, option A is the only question that can be tested using quantitative methods, such as statistical analysis. The question in option A states: "How does changing the amount of water affect the growth of corn?". This question is easily testable using scientific investigation, because controlled or measured amounts of water can be added to corn, and the consequent growth rate of corn can be easily measured and recorded. However, the questions in options B, C & D cannot be precisely measured using quantitative tools, since they aim to measure qualitative (subjective) factors, such as: ethics, happiness and disappointment.
Rheumatic fever is a disease that caused by Group A streptococcus infection. The bacteria has component that similar to the heart valve cells, makes the immune cell attack it. The drug of choice for this infection is penicillin G benzathine injection. It is one of penicillin family drug that has high prevalence of allergy reaction, so you must be aware.
