alternation

The different interlacement and alternation of all above four kinds of rhythm speeds make daedal narration rhythm.

以上四种节奏速度不同穿插和交替运用，可以构成千变万化叙述节奏。

Filter bed should be exposurd as less as possible because alternation of exposure and immersion is disbennifit to the penetrability of filter bed.

依据水质资料分析了水源水质安全保障。