B. Because his beloved's beauty is as transient as the morning dew.
Explanation:
In the given lines from <em>To His Coy Misstress,</em> the speaker compares his beloved's<em> youthful hue</em> (youthful skin) to <em>morning dew.</em>
Dew is water that we can see in the form of droplets on plants in the morning. It doesn't last long - it is usually gone by mid-morning, disappearing after the sun rises. This is why dew is often used as a symbol for youth and how transient it is. Human life is often compared to one day, with the morning symbolizing youth and the evening symbolizing old age. Youth is as impermanent as dew, and this is what the speaker wants to tell us about his beloved.
