单选题 All assembly line workers are advised to check ______ time cards to make sure their working hours are properly marked.
【正确答案】 B
【答案解析】[解析] 词汇：代词
1．这是一道词汇题，选项均由代词构成。
2．check是及物动词，不能直接接宾格，C选项排除。
3．空格后出现名词(time cards)，因此所有格B．their为正确选项。