"""PARTIEL BUG"""
from collections import defaultdict
import heapq

class Graph:
    def __init__(self, n):
        self.graph = defaultdict(list)
        self.n = n
        self.seats = None

    def set_seats(self, seats, n):
        self.seats = [(i in seats) for i in range(n)]

    def add_edge(self, u, v, weight=1):
        self.graph[u].append((weight, v))

    def bfs(self, s):
        heap = []

        visited = [False] * (self.n + 1)

        heapq.heappush(heap, (0, s))
        visited[s] = True

        while heap:
            prio, s = heapq.heappop(heap)
            if self.seats[s]:
                return prio

            for w, v in self.graph[s]:
                if not visited[v]:
                    heapq.heappush(heap, (w+prio, v))
                    visited[v] = True

        return float("inf")

def main():
    # nb of seats, V, E
    k, n, m = map(int, input().split())

    # Prepare Graph
    students = [int(i)-1 for i in input().split()]
    seats = [int(i)-1 for i in input().split()]

    g = Graph(n)
    g.set_seats(seats, n)

    for i in range(m):
        a, b, c = input().split()
        g.add_edge(int(a)-1, int(b)-1, weight=int(c))


    # BFS from each of the students to determine the fastest
    dists = []
    for st in students:
        dists.append(g.bfs(st))

    mini = float("inf")
    best = -1
    for i in range(k):
        if dists[i] < mini:
            mini = dists[i]
            best = i
        elif dists[i] == mini:
            return "impossible"

    if best == -1:
        return "impossible"

    return students[best]+1




for _ in range(int(input())):
    print(main())