21.   There was a big Hornby train set, working by battery, with a set of rails to match, for Jerry.

22.   They work by creating a powerful alkaline solution which dislodges fats.

23.   They work by forming an invisible barrier to prevent water loss.

24.   Weighing machines work by measuring the amount by which a spring is compressed when some one stands on it.

25.   The drug works by walling off the bacteria from the other cells, so that they cannot affect the rest of the body.

26.   The drug works by increasing levels of serotonin in the brain.

27.   The switch works by passing a pulse of current between the tip and the surface.

28.   By day he worked downtown for American Standard.

29.   They work by bouncing microwaves off solid objects.

30.   The Action Group worked by dividing its tasks among a large number of subgroups.