description: 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. e. 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 ≠ 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.
  
  Input
  
  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 ≠ 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.
  
  Output
  
  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).
  
  Example
  
  Input
  
  
  3
  
  4 2
  1 2
  2 3
  2 4
  
  3 3
  1 2
  2 3
  
  5 3
  1 2
  2 3
  2 4
  4 5
  
  
  Output
  
  
  6
  0
  1
solution: import sys
  
  input = sys.stdin.readline
  
  F = [None]*101
  F[0] = 1
  for i in range(1,len(F)):
  	F[i] = (F[i-1] * i) % int(1e9+7)
  
  def rec(x, p, g, c, s):
  	c[s] += 1
  	for v in g[x]:
  		if v != p:
  			rec(v, x, g, c, s+1)
  
  def solve():
  	input()
  	n, k = map(int, input().split())
  	g = [[] for i in range(n+1)]
  	for i in range(n-1):
  		u, v = map(int, input().split())
  		g[u].append(v)
  		g[v].append(u)
  	MOD = int(1e9+7)
  	if k == 2:
  		print((n * (n-1) // 2) % MOD)
  		return
  	r = 0
  	for x in range(1,n+1):
  		d = [[0]*n for i in range(k+1)]
  		d[0] = [1]*n
  		for v in g[x]:
  			c = [0] * n
  			rec(v, x, g, c, 0)
  			#print(x, v, c)
  			for i in range(k-1,-1,-1):
  				for j in range(n):
  					d[i+1][j] = (d[i+1][j] + d[i][j] * c[j]) % MOD
  		#print(x,d)
  		for j in range(n):
  			r = (r + d[k][j]) % MOD
  	print(r)
  
  for i in range(int(input())):
  	solve()
  