Under the caste system, an individual a)
Can advance up the social ladder during this life if he or she works hard
b)
Can move up if they pass the civil service exam
c)
Must live according to the duties of the caste into which he or she is born
d)
May be asked to join a higher caste if he or she pleases people in higher castes

Why is the huronian supergroup rock formation particularly interesting to scientists? because it looks like a cross-section of a giant, stone encyclopedia because it formed during the period when oxygen began to accumulate in the atmosphere because it contains unusually large amounts of oxygen and sulfur because it dramatically altered the planet's development when it first formed