重点讲解：
1. break down （使）（物质）分解；
Sugar and starch are broken down in the stomach.
糖和淀粉在胃里被分解iqny!kRrcN8R-,ZlmAZq。
2. build up （使）积聚；（使）逐渐增加；
Slowly a thick layer of fat builds up on the pan's surface.
慢慢地，平底锅表面积起了一层厚厚的油脂XOoe=+6qN5J-r;。
3. in the middle of (某件事或某段时间的)中期；
I had a little lapse of concentration in the middle of the race.
我在比赛中途一时走神MP4YibwdabzwMeX2_。
4. at hand （空间或时间上）接近的，不远的；
Having the right equipment at hand will be enormously helpful.
手头上有合适的设备将会帮上大忙q7njcN*gc@IaE。