A.a barB.a dropC.a loafD.a piece

As shown, object A and B with mass of m1 and m2 are put on a smooth surface of a table and they are connected through a light spring. Another two objects C and D are on objects A and B, and the frictional factors between A and C, B and D are not equal to zero. An external force pushes on A and B along the horizontal direction and the spring is compressed. As removing the external force during the process of A and B being apart away， for the system of A, B, C, D and the spring we have（ ）

A、Both momentum and mechanical energy are conserved;

B、Momentum is not conserved while mechanical energy is conserved;

C、Both momentum and mechanical energy are not conserved;

D、Momentum is conserved , while mechanical energy is not necessarily conserved.

A.transferred

B.offended

C.impressed

D.bothered

A.take in

B.take out

C.take up

D.take over

A.They may have been caused by the damage to the radio system．

B.They may have taken place during take-off and landing．

C.They were proved to have been caused by the passengers’portable computers．

D.They were suspected to have resulted from electromagnetic interference．

A.was an efficient way of organizing work

B.was an important development in methods of production

C.inevitably led to economic development

D.increased the production of existing goods

A.informing

B.having informed

C.to inform

D.to have informed

A.I ean，t stand it

B.Sorry to do it

C.I hate to compiain

D.Sorry to bother you

A.to have closed

B.to close

C.having closed

D.closing