Read the excerpt from "Ship's Chronometer from HMS Beagle.” Just as people adopted a common standard time, so numerous aspects of working and daily life were becoming rigidly fixed by the clock, from clocking on at work to school hours and tea-time – which is the subject of our next chapter.

What context clue best helps readers determine the meaning of the word standard?
a. “numerous”
b. “rigidly fixed”
c. “tea-time”
d. “subject”