未知题型 By saying 'a variant on the formula' (Line 1, Paragraph 4), the author means thatA.luxury-car rental is a new business.B.foreign car-rental business is different from luxury-car clubs.C.rental-car companies run in different ways.D.rental-car business is newly developing.

未知题型 The 'prestige Collection' business of Hertz isA.decreasing,B.just about to begin.C.absolutely making gooD.D.gaining some profits.

单项选择题 补体在血清中含量最高的成份是 A、C1 B、C4 C、C3 D、C2