The only correct answers are A and E. All mammals do have hair, and mammary glands. Mammals also have jaws, though spiny anteaters have toothless jaws. This renders them incapable of chewing their prey. Instead, they swallow ants and termites whole.
B is incorrect because not all mammals have a placenta. Marsupials, like Kangaroos, skip the placental stages of pregnancy and instead the young develop inside the mother's pouch. And some mammals don't even do that, the duck-billed platypus is oviparous i.e. it lays eggs. That's right platypus lays eggs like birds and reptiles, but it is still a mammal because after the eggs hatch, the mother feeds the babies with milk from her mammary glands.
C. is also incorrect because as noted, some mammals are oviparous, and lay eggs, amniotic egg is characteristic of viviparous animals (i.e. those giving birth to live young).
D. Is incorrect because not all mammals have opposable thumbs. Humans, primates (apes and monkeys), and Koalas all have opposable thumbs; but cows, deer, and whales are all mammals and do not have opposable thumbs.