Always use the safety belt and buckle your child in immediately after putting her in the booster seat. Even if your child's belted in safely, never leave her sitting in a booster seat unattended. Hold off on using booster seats without belts, such as the plastic cube-shaped seats you often see in restaurants, until your child's about 36 months old. These seats are not only dangerous because they lack safety belts, but they're also missing straps for securing the booster to a chair.
Noun. 1. trough-a narrow depression (as in the earth or between ocean waves or in the ocean bed). natural depression, depression-a sunken or depressed geological formation. swale-a low area (especially a marshy area between ridges).
A wave is an up and down movement of water. When we talk about waves, we use special words to name their parts. The highest point of a wave is called the crest. The lowest point is called the trough. Wave height is the vertical distance between the crest and trough. Wavelength is the horizontal distance between waves in a series. Wavelength can be measured between two wave crests. It can be measured between two wave troughs.