(2) A math book is 6 mm thick;

(3) Flight speed of aircraft1800km;

(4) The school playground runway is 400 meters long;

(5) Dad weighs 70kg.

(6) An orange weighs 50 grams;

The load capacity of a car is 4 tons.

So the answer is: centimeters, millimeters, kilometers, meters, kilograms, grams, tons.