Correct Answer: Ancient

Solution : The correct choice is the second option.

A novel refers to something new, original, or innovative. Ancient stands in contrast to the antonym, signifying something old, historic, or from a distant past.

The meanings of the other options are as follows:

• Formal : This means following established conventions or procedures.
• Traditional : This relates to customs, beliefs, or practices passed down through generations.
• Customary : This refers to what is usual or habitual according to a particular custom or tradition.

Therefore, the correct answer is ancient.