单选题 The teacher ______ his fingers on the desk impatiently while waiting for the student's answer.
【正确答案】 D
【答案解析】[分析] 近义词辨析 A．spray．喷射，喷溅；B．nod点头；C．rock摇动；D．tap轻打，轻敲，开发，分接，使流出；因此选项D为答案。