Complete the sentences, using -ing forms. 1. There are only some advantages of ...
2. Customs and law enforcement authorities in particular benefit from ...
3. Customs authorities can no longer afford ...

 1.They were happy to get the invitation letter, weren't they?                                2.Yesterday your friends went to the cinema, didn't they?                                    3.The group of students won't stay in the hotel, will they?                                    4.His collection of stamps was the best, wasn't it?                                                5.Head Teacher didn't write the letter, did he/she?                                                6.We can arrange a date and time right now, can't we?

1) Trigonometric levelling consists in computing the difference in elevation of
two points on the basis of horizontal distance and the vertical angle between
them, doesn't it?
2) Is it usually combined with the triangulation work, the vertical angles being
measured at the same time as the horizontal angles?
3) What is measured to some definite point on the signal the height of which above the station was determined when the signal was erected?
4) Should the height of the instrument above its own station also be measured and recorded?
5) Are in a very precise work angles measured with a special vertical circle
instrument?
6) Are the best results obtained by averaging several independent readings half of which are taken with the telescope direct and other half with the telescope inverted?
7) The chief difficulty in obtaining accurate results by trigonometric levelling
is the uncertainty in the coefficient of refraction of the air, isn't it?
8) What can be eliminated is by taking simultaneous observations between two
stations?
9)  What consists in computing the difference in elevation of two points on the basis of horizontal distance and the vertical angle between them?
10) What results are obtained by averaging several independent readings half of which are taken with the telescope direct and other half with the telescope inverted?