His door was opened on the first 【summon】; and he appeared in person, unarmed, and in a peculiarly defenseless condition.
A、concern
B、service
C、summary
D、call
【正确答案】：D
【名师解析】:题目中的关键词"summon"在这里指的是"召唤"或"召集"。根据句子的语境，"His door was opened on the first summon"意味着第一次有人召唤他时，他就打开了门。这表明他响应了某种"call"或"召唤"。因此，选项D "call"是正确的答案，因为它最符合句子中"summon"的含义。其他选项A "concern"（关心）、B "service"（服务）、C "summary"（总结）都与"summon"的含义不符。
