A haploid cell is a cell typically with half the number of chromosomes (a sex cell) used for reproduction.
A diploid cell is the opposite, a full set of chromosomes not intended for sexual reproduction but typically used in mitosis.
Well, pollution is probably the main reason, but i think all of them are reasons why animals are dying off, if there isn't any choice for all of them, then your best bet would be to do a, pollution.