16．We find such shrubs____ will best stand up to（抵御）hard weather．

    A．which                        B．as

    C．what                     D．who

17. Mrs. Douglas unknowingly left a package____on the shop counter.

    A．laying                   B．to lie

  C．laid                       D．lying

18．____that called this morning？

    A．Who was                       B．Who it was

    C．Who was him                   D．Who was it

19．Earthworms occur_____adequate moisture and food and the necessary soil

    conditions are found.

    A．and                  B．whenever

C．however                  D.wherever

20. None of the soldiers was allowed to open fire unless heavy loss was shown to be___      inevitable．

A.nonetheless                           B.otherwise

C.hence                                 D.therefore