Why do environmental scientists use systems and diagrams to explain process in ecosystems

Ineed to know why d is the correct answer asap

Which organisms have pharyngeal arches that develop from all three germ layers and go through the same development stages as embryos? 1.bird 2.ladybug 3.starfish 4.snake

During the process of two rails or sides break apart and attract new nucleotide bases to form a new and complete strand.