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 io,os
  input = io.BytesIO(os.read(0, os.fstat(0).st_size)).readline
  from collections import deque
  
  M = 10**9+7
  
  def gettot(dic,k):
     
      nums = []
      for key in dic:  nums.append(dic[key])
  
  #    print(nums)
      m = len(nums)
  
      dp = [[0 for j in range(k+1)] for i in range(m+1)]
      for i in range(m+1):  dp[i][0] = 1
      
  
      for i in range(m-1,-1,-1):
          for j in range(k+1):
              if m-i<j:  break
              dp[i][j] = dp[i+1][j] 
              if j>0: dp[i][j] += nums[i]*dp[i+1][j-1]%M 
              dp[i][j] = dp[i][j]%M
  
      return dp[0][k]
  
  
  #dic = {0:4,1:3,2:2,3:2}
  #print(gettot(dic,4))
  
  
  
      
  
  
  def main(t):
  
      s = input()
      n,k = map(int,input().split())
      neigh = [[] for i in range(n)]
      for _ in range(n-1):
          u,v = map(int,input().split())
          neigh[u-1].append(v-1)
          neigh[v-1].append(u-1)
  
      ans = 0
      if k==2:  
          print(n*(n-1)//2)
          return 
  
  
      for root in range(n):
          queue = deque()
          layers = [{}]
        
          for ele in neigh[root]:
              queue.append([ele,ele,root,0])
              layers[0][ele] = 1
          
          while queue:
              [index,ancestor,father,l] = queue.popleft()
              for nextindex in neigh[index]:
                  if nextindex==father: continue 
                  if l+1==len(layers): layers.append({})
                  if ancestor not in layers[l+1]: layers[l+1][ancestor] = 0
                  layers[l+1][ancestor] += 1
                  queue.append([nextindex,ancestor,index,l+1]) 
  
  #        print(layers)
          
          for dic in layers:
              if len(dic)<k: break
              ans += gettot(dic,k)
              ans = ans%M
              
              
          
  
      
  
  
  
  
  
  
      print(ans)
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  T = int(input())
  t = 1
  while t<=T:
      main(t)
      t += 1