????? ???? ??? ??? 1?? ????(20).

??? 4? ??11?? ?? ??? ??? ??? ??? ??? ? ???? ??? ??? ??? ???(12·?1)? ???(13·?1), ??? ??(12·?·??6?) ? 3?? ??? ??? ????? ?? ????.

???? ???? ??? ?? ?? ??? ???? ????? 40～50m ???? ??? ???? ??? ???? ????? ??? ??? ???.

?? ????? ?????(49)? ??? ??? 3? ???? ???, ??? ??? ?? ? ?? 13?? ?? ??? ??? ?? ???.

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