When cracked, the concrete absorbs moisture from surrounding air, then becomes soft and "grows," filling in the crack.
出现裂纹以后，混凝土会从周围的空气中吸收水蒸气，变软进而“生长”，从而将裂缝填充起来。
2
To you, leaving that window open just a crack during the day is a way to let in a little fresh air.
对于你来说，在白天把窗户打开出一条缝隙是为了呼吸一点新鲜空气。
3
The Mother Birch had hardly spoken these words than a terrible, deafening crack shook the air, and a sharp, hot tongue of lightning landed right on her trunk.