Sentence Completion

English as a Second Language English Vocabulary, Grammar and Idioms
1

Please need explanation on grammar.

  1. The trapdoor spider lives underground__________catches insects which
    walk near its secret door.
    (A) except
    (B) and
    © besides
    (D) since

7._________an earthquake occurs that measures 7.0 on the Richter scale, its effects can be felt 400 kilometers away.
(A) When
(B) Why
© What
(D) How

  1. _________burns, it gives off a toxic gas.
    (A) Petroleum
    (B) When petroleum
    © Whether petroleum
    (D) Petroleum that

9.________heated to the proper temperature, it shrinks and hardens.
(A) Is clay
(B) Clay
© Clay is
(D) If clay is

  1. As primitive societies became more sophisticated,________a
    standardized system of weights and measures.
    (A) for the need arising
    (B) the need arose for
    © the need arising for
    (D) arose for the need
2

I’d like to have your answers first, 6) to 9) being quite elementary.