请详细说明原因.

If you're(      )in Spain,do come and see me.
A.ever   B.never    C.once     D.nearly

This book is (      )more useful for us students?Yes,but it is (      )too difficult.
A.quite,quite   B.much,much      C.rather,quite     D.quite,much

   3.He doesn't sing (       )that night ae he usually does.
       A.so well   B.so better      C.more better    D.so best
  4.Jack writes (      ) than he did before.
     A.much carefully     B.more  carefully      C.much more carefully     D.much carefully