14．I used to swim with my friends in this river summer and fall, but not once since I left my hometown in 1998 ________.
A．I have swum B．I swam
C．did I swim D．have I swum
答案 D [否定词not置于句首，主句用倒装语序。从since从句中可推断出主句应该为现在完成时态。]
15．We'll have to think twice before we decide to buy a product an advertisement ________.
A．suggests B．shows C．makes D．praises
答案 A [suggest在本句中意为“推荐，举荐”。 ]
