In hypothesis testing, a statement that there is no difference between populations is the __________

Children who develop into successful, happy adults who are generous with others tend to be reared by ______ parents

Fill in the blank with correct word

Some research questions cannot be answered using human experiments because

a. some studies would be impractical or unethical. b. randomization is often hard to achieve. c. double-blind studies are usually dangerous to participants. d. researchers know that their results usually will not be published. e. they are not a very effective way to learn about cause and effect relationships.