(    )6.The stones they carried were used         houses and bridges.

A.to build       B.for building      C.to be built     D.Both A and B

(    )7.He         here since breakfast.

A.must come     B.must have been     C.have come     D.must be

(    )8.At that time I noticed him         past.

A.walk      B.to walk      C.walked      D.walking

(    )9.I         all the exercises before our teacher collected them.

A.have finished      B.finished     C.had finished     D.finish