1.cavity n. 腔；洞，凹處

如：The heart without knowledge is a cavity.
沒(méi)心知識(shí)的心是一個(gè)空洞。

2. stuck with 被……纏住

如：Why am I always stuck with the washing-up?
干嗎總是要我洗餐具?

3. reversible adj. 可逆的；可撤消的；可反轉(zhuǎn)的

如：The machine also possesses a reversible fabric guide and optimized trough suitable for woven fabric and knitwear.
此機(jī)器同樣擁有可逆的導(dǎo)布器和適合于機(jī)織物和編織物的最佳染槽。

4.harden 使…變硬；使…堅(jiān)強(qiáng)；使…冷酷；使…麻木不仁

如：With the temprature cool, magma would be hardened into rock.
溫度越來(lái)越低，巖漿也就變硬，最后成了巖石。

5.fluoride n. [化]氟化物
6.tooth decay 蛀牙；齲齒；齵齒

如：One major problem is tooth decay.
一個(gè)主要的問(wèn)題是蛀牙。

Too little brushing and too many sweets can cause tooth decay, sometimes very seriously.
極少刷牙和吃太多的糖果會(huì)導(dǎo)致蛀牙，有時(shí)會(huì)非常嚴(yán)重。