Asustained muscle contraction is referred to as what ?

(05.01 mc) west indian manatees are large aquatic mammals that live in rivers and near shore estuaries, especially in florida. they have two flexible front flippers with three or four toenails, similar to elephant toenails. though they lack hind limbs, manatees have vestigial pelvic bones, as shown in the diagram. manatee and elephant skeletons are shown side-by-side. the manatee, an aquatic animal, has a skeleton that has two large front limbs and two very tiny hind limb bones that do not form actual limbs. the elephant has four large limbs. which of the following answer choices best describes how evidence of the manatee toenails and pelvic bones supports the scientific theory of evolution of these animals? (1 point)