Explanation:

A mare's nest:
An idea or a discovery that seems interesting and exciting but is found to be false or have no value.

Ex. I fancy this will prove to be a mare’s nest! We have had these mysteries before.

Ex. In a global socio-economic order dominated by the striving for private profit, together with the divergent aims of capitalist nation-states and imperialist great powers, the project has already become a mare’s nest of conflicting interests.

Option A is hence the correct answer