As atp binds to the myosin head at the beginning of a muscle contraction cycle, the myosin head immediately a. detaches from actin. b. initiates binding with actin. c. tightens its bond to actin. d. swivels.

i dunno but  i think its b

blah

explanation:

bc blah

the corpus luteum secretes estrogens and progesterone. the latter hormone causes changes in the uterus that make it more suitable for implantation of the fertilized ovum and the nourishment of the embryo. if the egg is not fertilized, the corpus luteum becomes inactive after 10–14 days, and menstruation occurs.

i hope this : )