Which of the following is a testable hypothesis?

A. Altered temperature may affect gas production, which measures fermentation rate.

B. Does temperature affect fermentation?

C. Temperature decreases will affect gas production and fermentation much of the time.

D. If temperature is increased, then gas production, which measures fermentation rate, will increase.

D is easily testable, and replicable.

The testable hypothesis among the options provided is:

D. If temperature is increased, then gas production, which measures fermentation rate, will increase.

The testable hypothesis among the given options is option D: "If temperature is increased, then gas production, which measures fermentation rate, will increase."

A testable hypothesis is a statement that can be tested or proven true or false through an experiment or observation. In this case, the hypothesis can be tested by conducting an experiment where the temperature is varied, and the resulting gas production is measured and compared.

To determine if a hypothesis is testable, it should have a cause and effect relationship, and it should be possible to manipulate or change the variables involved. In option D, the hypothesis states that if the temperature is increased, there will be a corresponding increase in gas production (which is a measure of fermentation rate). This cause and effect relationship can be tested by manipulating the temperature and observing the resulting gas production.

In contrast, options A, B, and C are not as directly testable. Option A states that altered temperature "may" affect gas production, which is not specific enough to clearly define a cause and effect relationship. Option B is a question rather than a statement, so it cannot be tested directly. Option C suggests that temperature decreases will affect gas production and fermentation "much of the time," which is vague and does not provide a clear prediction that can be tested.