Answer:
B . Mesoderm
Step-by-step explanation:
The germ layers begin to develop from the fourth to the seventh week, in this period one has an embryo. All cell types will derive from these layers called ectoderm, mesoderm and endoderm.
Mesoderm which is the middle layer of the embryo forms the dermis, smooth and skeletal muscles, the circulatory system: heart, blood vessels, lymphatic tissue, connective tissue; the skeletal system: bones and cartilage; and the excretory and reproductive system: genitals, kidneys, urethra, bladder and gonads.