题目

Tom is good at his work, but he seems to _____ confidence. A. lack  B. lack of   C. lacking in  D. short of 答案：A 解析: 略（本题11分）在△ABC中，角A、B、C的对边分别为、、，且（1）判断△ABC的形状；（2）设向量=（2，） ， =（，-3）且⊥，（+）（-）=14，求S△ABC的值。