21.   The anti-collision systems can measure distance between aircraft, speed and altitude and warn air traffic controllers on the ground in advance.

v. + distance >>共 200
keep 30.28%
go 10.30%
travel 7.48%
put 6.64%
walk 4.35%
maintain 2.67%
drive 1.75%
cover 1.75%
have 1.60%
measure 1.60%
measure + n. >>共 1032
success 3.68%
performance 2.60%
progress 2.45%
level 2.40%
amount 2.02%
effect 1.78%
change 1.75%
number 1.34%
effectiveness 1.17%
impact 1.11%
distance 0.61%
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