There are 3 cm, 4 cm, 6 cm, and 7 cm long sticks. Choose three sticks to form a triangle. How many triangles can be formed? how many kinds
有3厘米、4厘米、6厘米、7厘米长的小棒各一根，选择其中的三根小棒围成一个三角形，一共可以围成多少种三角形？多少种
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