(1)(a)→(r),(b)→(q),(c)→(p),(d)→(s)(2)(a)→(r),(b)→(p),(c)→(s),(d)→(q)(3)(a)→(r),(b)→(s),(c)→(p),(d)→(q)(4)(a)→(r),(b)→(s),(c)→(q),(d)→(p)