There are certain _______when you have to interrupt people who are in the middle of doing something.

The system has been designed to give students quick and easy ____  to the digital resources of the library.

Before Tom left home, his mother kept telling him to ________ his manners at the party.

The faces of four famous American presidents on Mount Rushmore can be seen from a ____ of 60 miles.

(2014·山东省十二校高三联考)Much to our surprise，the witness’s________of the traffic accident differed from the official version in several aspects.