B'A tree is an undirected connected graph without cycles. You are given a tree of n vertices. Find the number of ways to choose exactly k vertices in this tree (i. xe2 x80 x89e. a k -element subset of vertices) so that all pairwise distances between the selected vertices are equal (in other words, there exists an integer c such that for all u, v ( u ne v , u, v are in selected vertices) d_{u,v}=c , where d_{u,v} is the distance from u to v ). Since the answer may be very large, you need to output it modulo 10^9 + 7 . The first line contains one integer t ( 1 <= t <= 10 ) -- the number of test cases. Then t test cases follow. Each test case is preceded by an empty line. Each test case consists of several lines. The first line of the test case contains two integers n and k ( 2 <= k <= n <= 100 ) -- the number of vertices in the tree and the number of vertices to be selected, respectively. Then n - 1 lines follow, each of them contains two integers u and v ( 1 <= u, v <= n , u neq v ) which describe a pair of vertices connected by an edge. It is guaranteed that the given graph is a tree and has no loops or multiple edges. For each test case output in a separate line a single integer -- the number of ways to select exactly k vertices so that for all pairs of selected vertices the distances between the vertices in the pairs are equal, modulo 10^9 + 7 (in other words, print the remainder when divided by 1000000007 ). '...