Received a PM asking me to respond specifically as to the issue with C.

as myohmy mentions, if C were correct, it would read "a chalice was buried to avoid being stolen..."

The chalice was buried by someone else, right? (That is, it did not bury itself. ) That's why the sentence is in passive form: "was buried."

The "to avoid" part - is that something that the chalice is doing? Nope. Someone else wants to prevent it from being stolen, right? So, a person can do something to avoid something else. Or a person can prevent something from happening to an object. Or an object can have something done to it to prevent something else from happening to it. But this sentence (with choice C) says that the object has something done to it in order to avoid something else happening to it. The problem here is that the object cannot avoid having something else happen to it - the object is passive. Either a person is doing something to avoid something else, or an object is having something done to it to prevent something else from happening to it.

I'd generally chalk this up to idiom, except that it's not quite an idiom - it's more language usage and the real test generally tries to avoid that kind of stuff as much as possible nowadays because they are trying to reduce the bias against non-native speakers. So I wouldn't worry too much about this one.

Curious - where did this one come from? It seems like a generally well-written question but out of date. Maybe from an old paper test or just a really old question from a test-prep company?