21.   A. The simple explanation is that Easter usually falls on the first Sunday after the first full moon that occurs after the vernal equinox.

22.   A. The simple explanation for the turnover rate is supply and demand.

23.   But in his briefing, the mayor suggested a simple explanation.

24.   But that simple explanation is hardly complete.

25.   But one or two simple explanations are very seductive.

26.   But there is a simple explanation, and one that suggests the end may be in sight.

27.   But the surge of dogs on TV defies one simple explanation, or any one-dimensional role.

28.   But underlying that simple explanation is a complex of puzzling factors that leave everyone, television programmers and viewers alike, exasperated and yearning for the old days.

29.   Can you give me a simple explanation of how to prune grapes?

30.   Clicking there will take you to some sites, mostly maintained by universities, that will help give you a relatively simple explanation of some basic laws and theories.