Final answer:
The alternative hypothesis is the statement contrary to the null hypothesis and is both the hypothesis of interest for researchers and the one accepted if the null hypothesis is rejected.
Step-by-step explanation:
The alternative hypothesis (notation Ha) is the statement in hypothesis testing that is contrary to the null hypothesis (notation H0). It represents the hypothesis of interest that researchers are seeking to support. When the null hypothesis is rejected through statistical tests, the alternative hypothesis is the one that is considered to be indicating an observed effect or difference. Therefore, the correct answer to what the alternative hypothesis is would be both option b) The hypothesis of interest of researchers and option c) Hypothesis accepted when the null hypothesis is rejected.