Answer:
d. Researchers said the flu shot reduced the risk of developing the flu when it actually didn't.
Explanation: The rejection of true null hypothesis based on experimental procedures is called Type 1 error.
The primary aim of the investigation was to find out if a flu shot guide against flu infection or not.Therefore to arrive at a conclusion, this true null hypothesis must be tested, and evidences of the effects of flu shot on development of flu could be determined.
Therefore after testing;evidences arrive at will determine if flu shot reduces the risk or no effect at all.However, if there is no significant evidence to support the potency of flu shot, and it was jumped to conclusion that its actually reduces the risk of development,(that is null hypothesis was rejected) then the basis for the test- which is to test the null hypothesis has been defeated, thus Type 1 error has been committed .
When the researcher concluded that flu shot actually reduced the risk,when actually it was the contrary, he had rejected the objective of the true null hypothesis .Besides there was no probability value to show that this was below 0.05 confidence value.