单选题 The conversation had been (carried on) chiefly (in French), a language (which) Mr. Steward was (perfectly) acquainted.

【正确答案】 C
【答案解析】改为with which.因为which所代表的先行词language在定语从句中是be acquainted with后的宾语,此处with不可省,故放于which前,改为with which.