题目

— Be careful when you go ________ the street.— Thank you. I will look left and right before I ________ the road.A. cross; cross B. across; across C. cross; across D. across; cross 答案：【答案】D【解析】句意：——当你过马路时要小心。——谢谢。过马路前我要左右看。cross动词，意思是“横渡，横跨”；across介词，意思是“穿过，横穿”。go across穿过，第一个空缺少介词；第二个空缺少谓语动词，需要用cross，故答案为D。（1）已知R为全集，A={x|-1≤x＜3}，B={x|-2＜x≤3}，求（CRA）∩B；（2）设集合A={a2，a+2，-3}，B={a-3，2a-1，a2+1}，若A∩B={-3}，求 A∪B．