21．(2012·太原第一学段测评)As Susan stared at________piles of plastic in her recycling bin，________strong sense of responsibility made her stick to her recycling work.
A．不填；不填 B．不填；a
C．the; a D．the; the
答案：C 考查冠词。第一空特指她垃圾箱的那堆塑料，所以用定冠词；第二空a sense of responsibility“一种责任感”。
