（）20 targets can be tracked at one time．When maximum tracking capacity is reached，no further acquisitions are possible.

For one or two types of engine, the piston and rod can be withdrawn downwards from the cylinder into the crankcase and then out through the （）.

For one or two types of engine,the piston and rod can be withdrawn downwards from the cylinder into the crankcase and then out through （）.

DSC distress relays can be transmitted by either（）or（）.

A block that can be opened at the hook or shackle end to receive a bight of the line is a（）.

It’s（）to stow optional cargo in the lower hold．You’d better give it block stowage in the tweendecks，then it can be easily discharged either at Shanghai，or Dalian or Tianjin.

In(74), the only element that can be deleted or removed is the one that was inserted most recently.

● In （74） the only element that can be deleted or removed is the one that was inserted most recently.（74）

A body can only be observed at lower transit when（）.

—Look at these tracks. It __________ be a wolf.
   —It needn't be. It __________ be a fox.( )

Which constraint can be defined only at the column level? （）

Which constraint can be defines only at the column level? （）