单选题 He tried to ______ up his lessons by telling a few jokes.
【正确答案】 D
【答案解析】(liven使活跃起来，与up连用)。句意为：他讲了几个笑话，力图让课堂气氛活跃起来。A．raise提高；B．stimulate刺激；C．inspire激励。