The first textbook ______ for teaching English as a foreign language came out in the 18th century.
【正确答案】 D
【答案解析】过去分词用法,此处作后置定语修饰textbook,textbook与write之间存在被动关系,排除A,正确答案为D,相当于which was written。to be written指将要进行的动作,being written强调动作的进行状态,不符合句意。