题目

胚胎发育的正确顺序是（    ） ①组织分化             ②受精卵分裂               ③形成胚泡   ④器官形成             ⑤形成胎儿                 ⑥分娩 A．①②③④⑤⑥      B．②①④③⑤       C．②①④⑤③⑥      D．②③①④⑤⑥                                                                            听音填空。1. _____________ points up.2. _____________ points down.3. _____________ points left.4. _____________ points right.5. Look at this _____________.