The nurse teaches the parents of a child being treated with antibiotics for an ear infection for a follow-up visit after the child completes the course of therapy. Which of the following statements by the parents indicates that they understand the reason for the follow-up visit

A. "Her hearing needs to be checked to see if the infection has done any damage. "
B. "The doctor wants to make certain she has taken all the antibiotics. "
C. "We need to make sure that her ear infection has completely cleared. "
D. "She needs to get another prescription for second course of antibiotics. "

同学们为了探究水的组成，用如图所示的装置进行实验。通电后两电极都有气体放出，经检验甲试管里的气体能燃烧，乙试管里的气体能使带火星的木条复燃。若氢原子模型用“ ”表示，氧原子模型用“  ”表示，则构成甲试管中气体微粒的模型可表示为（  ）