Umbrascopy
X线透视检查
🗣️ 情景例句
You're OK, Dad.
你真好，爸爸。
Many a little makes a mickle.
积少便成多。
and a period (which is the time it takes a wave crest to travel one wave length).
和周期（浪峰走过一个波长所需的时间）。