periodic law of chemical elements

例句：

1. 1. The temperature in this area is periodic with highs and lows.
   这个地区的温度是周期性的，有高有低。
2. 2. The sun's rays are periodic, shining at different times of the day.
   太阳的光线是周期性的，一天中不同时间会照射。
3. 3. The moon's phases are periodic, changing every 29.5 days.
   月亮的相位是周期性的，每29.5天变化一次。