at his knowledge, all the students showed their respect for their teacher.
A. Amazed
B. Being amazed
C. Amazing
D. Having amazed
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(答案→)A. Amazed
B. Being amazed
C. Amazing
D. Having amazed
解析：考查形容词用法。固定词组be amazed at…对…感到惊讶；本题amazed at…是对主语all the students进行修饰的。句意：对于他的知识感到很惊讶，所有的学生都很尊敬他们的老师。故A正确。