Do males of all sexual species have y chromosomes?

Which of the following choices is not an effective solution to the energy waste related to inefficient lighting? a. using low-pressure sodium lighting sources b. pointing lights on billboards and street signs upward c. placing light sources on time controls d. shielding light to direct it downward

Why do you think the puppy litter was all dark-haired?

Which of the following is the earliest era of earth's geologic time scale? cenozoic mesozoic precambrian paleozoic