Before using any chemical in the lab, why should one first read the Material Safety Data Sheet (MSDS)? The MSDS provides information on safe handling of the chemical.
The MSDS explains where the chemical can be purchased.
The MSDS provides the chemical formula for the substance.
The MSDS describes how the chemical will react with other substances.

d

explanation:

the correct answer, according to e2020, is the second choice there is an occluded front in region a and a cold front in region b.

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.