例句：
The drug improved mental alertness.
这种药物提高了大脑的灵敏度。
That purpose is alertness.
这个目的就是警惕。
They also increase alertness and energy.
它们也能提高机敏性和精力。
It made some evolutionary sense, that state of alertness.
那种警觉的.状态会形成某种进化感。
Research has shown that the lavender scent increases alertness.
研究表明薰衣草香味会提高人的警惕性。