For this question, choose the option opposite in meaning to the word or phrase in italics. The robbers gained access to the bank because of their porous sec...

Porous means having tiny holes or gaps that allow liquid, air, or other substances to pass through. In the context of this sentence, "porous security network" means a security system full of weaknesses and gaps that allowed the robbers to gain access.

The word opposite in meaning is impermeable, which means not allowing fluid or other substances to pass through; completely sealed. An impermeable security network would have no gaps or weaknesses - the direct opposite of a porous one.

The other options are not antonyms:

• amorphous means without a clearly defined shape or form. This describes structure, not permeability.
• gorgeous means beautiful or very attractive. It has no connection to the concept of permeability or security gaps.
• pervious means allowing water or other substances to pass through - this is a synonym of porous, not an opposite.

Note the trap in this question: pervious looks like it could be an antonym because of the prefix, but it actually means the same as porous. The true opposite is impermeable (or impervious).