What did mendel's cross-pollination of pea plants prove?

a. each parent only passes on one-half of its hereditary factors to the offspring.

b. it takes four generations of offspring to determine the parents' factors.

c. there is no such thing as a true-breeding plant; they all have hidden factors.

d. inherited factors combine in offspring to make entirely new characteristics.

The correct answer would be A. Each parent only passes on one-half of its hereditary factors to the offspring.

It can be correctly explained with the help of the law of segregation.  

It states that the alleles of each gene get segregated from each other and each gamete produced by a parent would contain only one out of two alleles of a gene.

For example, if the genotype of a parent is Tt, then the gamete would contain either T or t.

Thus, each parent only contributes half of its heredity factors in the form of gametes.

what image you forgot to include it.

the oldest known insects are believed to live around 400 millions ago as suggested by the fossil records.   some plants having woody stems also evolved during this time.

after the evolution of insects the first four legged species or the tetrapods evolved in shallow freshwater habitats from the intermediate species approximately 397 million years ago. the tetrapods went on conquering the land giving rise to amphibians, reptiles, mammals and birds.

the major split in tetrapods first occurred 340 million years ago branching off from amphibians.

363 million years ago when the carboniferous period began the insects started roaming on land and taking flights, following which the four limbed tetrapods adapted in the terrestrial habitat.