题目

声音音调的高低与物体振动的 有关．向一个空暖水瓶中灌水，有经验的人凭声音就可知瓶是否灌满．这是因为水灌得越多，空气柱变得越 ，气柱发出的音调越 答案：【1】频率【2】短【3】高用所给单词的适当形式填空。 1. He was a natural leader, and when he ____ (command), everyone obeyed. 2. Theory ____ (base) on practice and in turn serves practice. 3. I am just ____ (request) that you keep him safe. 4. The girl ____ (recognize) her father and cried at once. 5. The meeting ____ (expect) to end in the morning.