What does the former Labour MP mean by saying "social mobility created falters as well as

What does the former Labour MP mean by saying "social mobility created falters as well as risers" in Paragraph Four？

A．Social mobility was a "two-way street" and "a zero-sum game".

B．All students from comprehensive school can reach the Oxford by hard work.

C．School dropouts always work with lower payments.

D．Social mobility was a mirror to constant efforts from different people.

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