III Skim the text to finish the sentences.
1 Prior to 1970, the best estimate was calculated from…………………………... 2 Now, a Kalman filter calculates the best estimate from……………………... 3 Digital maps, often stored on compact disc, are carried on………………….. 4 Military aircraft superimpose their navigated position on …………………... 5 Algorithms for waypoint steering and for …………………….…………….. 6 Specially equipped aircraft are often used for……………………………….. 7 Airborne test beds and hardware-software integration laboratories are……... IV Study the grammar point and practice, and if there are some find in the Text. GRAMMAR POINT
PRESENT PERFECT TENSE
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