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
  from collections import Counter
  
  mod=10**9+7
  
  FACT=[1]
  for i in range(1,2*10**5+1):
      FACT.append(FACT[-1]*i%mod)
  
  FACT_INV=[pow(FACT[-1],mod-2,mod)]
  for i in range(2*10**5,0,-1):
      FACT_INV.append(FACT_INV[-1]*i%mod)
  
  FACT_INV.reverse()
  
  def Combi(a,b):
      if 0<=b<=a:
          return FACT[a]*FACT_INV[b]%mod*FACT_INV[a-b]%mod
      else:
          return 0
  
  
  t=int(input())
  for tests in range(t):
      _=input()
      n,k=map(int,input().split())
      E=[[] for i in range(n)]
  
      for i in range(n-1):
          a,b=map(int,input().split())
          a-=1
          b-=1
          E[a].append(b)
          E[b].append(a)
  
      if k==2:
          print(n*(n-1)//2%mod)
          continue
  
      ANS=0
  
      for center in range(n):
          DIS=[-1]*n
          Q=[center]
          DIS[center]=0
          P=[-1]*n
  
          DISP=Counter()
  
          while Q:
              x=Q.pop()
  
              for to in E[x]:
                  if DIS[to]==-1:
                      DIS[to]=DIS[x]+1
  
                      if x==center:
                          P[to]=to
                      else:
                          P[to]=P[x]
  
                      DISP[(P[to],DIS[to])]+=1
                      Q.append(to)
  
          L=[[] for i in range(n+1)]
  
          for fr,dis in DISP:
              L[dis].append(DISP[fr,dis])
  
          #print(L)
  
  
          for l in L:
              if len(l)<k:
                  continue
              #print(l)
  
              DP=[0]*(k+1)
              DP[0]=1
  
              for x in l:
                  for j in range(k-1,-1,-1):
                      if DP[j]!=0:
                          DP[j+1]+=DP[j]*x
  
              ANS=ANS+DP[k]
              ANS%=mod
  
              #print(DP,ANS)
                  
      #print(ANS)
  
                  
  
                  
          
  
      print(ANS)
              
              
              
  