Mast cells can be mostly found inside your skin, airways and intestines.
肥大细胞通常集中在皮肤、气管、肠道中。
2
So musical instruments evolved in ways that optimize their acoustical properties, how the instrument vibrates and sends those vibration through the air to our eardrums.
因此，乐器的进化优化了它们的声学特性，且优化了乐器振动的方式，并将这些振动通过空气传到我们的耳膜。
3
Though we often hear about air crashes and serious casual deeds, flying is one of the safest ways to travel.