At Mathville Middle School, there were 50 students and 50 lockers. Each year for Pi Day (March 14), the students lined up in alphabetical order and performed the following strange ritual. The first student opened every locker. The second student went to every second locker and closed it. The third student went to every third locker and changed it (i. e. if the locker was open, the student closed it; if the locker was closed, the student opened it). In a similar manner, the fourth, fifth, sixth, . . . student changed every fourth, fifth, sixth, . . . locker. After all 50 students had passed by the lockers, which lockers were left open? HELP ASAP PLZZZ :C

Aresearch study is studying the effects of a new drug for osteoporosis alzheimer's disease (ad) for women above the age of 65 years. a group of individuals with osteoporosis is randomized into two groups. one group is treated conventionally, and the second group is treated with the new medication. assessments are made at 3, 6, 12, 36, and 48 months. the conventionally treated group is assessed for ad using a serum blood test, and the treatment group is assessed for ad using a pet radiotracer that binds to beta-amyloid plaques. in comparing these 2 trial arms, the authors of the study may encounter which type of bias? a. selection bias on the risk of developing b. measurement bias c. confounding bias d. recall bias e. lead-time bias