If the SD of a sample of scores is 5, which of the following includes all (and only) true statements? Group of answer choices a. The central tendency of scores is 5. b. On average scores are 5 units from the mean. c. This sample is less variable than one with an SD of 3. d. This sample is more variable than one with an SD of 3. a and b a and c a and d b and c b and d c and d all except a all except b all except c all except d