The researchers (i)____________ saw in crawfish frogs the behaviors, such as closed eyes or limbs tucked in toward the body, that indicate sleep in amphibians. Indeed, as is not the case for tree frogs and true toads, classic sleep behavior is (ii)____________ true frogs, including crawfish frogs, although bullfrogs, which are also true frogs, are quiescent at night. A. frequently B. beneficial for C. rarely D. undocumented in E. never F. common among