Step 1 :The null hypothesis (H0) is a statement of no effect, difference, or relationship. It is the hypothesis that the researcher is trying to disprove. The alternative hypothesis (H1) is a statement that contradicts the null hypothesis. It is the hypothesis that the researcher believes to be true and is trying to prove.
Step 2 :In this case, we are testing the claim that the mean amount of strontium-90 from city #1 residents is greater than the mean amount from city #2 residents. Therefore, the null hypothesis should be that the means are equal or that the mean of city #1 is less than or equal to the mean of city #2. The alternative hypothesis should be that the mean of city #1 is greater than the mean of city #2.
Step 3 :The correct hypotheses are: \[ H_{0}: \mu_{1} \leq \mu_{2} \] \[ H_{1}: \mu_{1}>\mu_{2} \]
Step 4 :So, the final answer is D. \[ \boxed{D} \]