a check on & a break on/an impediment to & a break on

[eee062010]

Source:
Practice Book for the Paper-based GRE® revised General Test
Second Edition

Each member of the journalistic pair served as ______ the other: each refrained from publishing a given piece if the other doubted that it was ready to be printed.
A a check on
B an advocate for
C an impediment to
D a brake on
E an apologist for
F an intermediary for

The answers are a check on & a break on. But I am wondering why not an impediment to & a break on?

[tommywallach]

Hey eee,

An impediment is something that is an actual problem. In this case, they aren't acting as impediments to each other, because they're doing it on purpose. They are slowing each other down for a positive reason (to make sure the best possible work comes out).

Hope that makes sense!

-t