Answer: b. selling VIX calls
Step-by-step explanation:
The client could make some money selling VIX calls. Call options give the holder the right to buy an underlying asset at a set price in future and they will do so if the market price of the underlying asset increases past the call price of the asset (exercise price).
If the client expects that market conditions will be stable then an increase in stock price is not expected. They can sell calls and make money from the premium they will charge for the calls knowing that they would not have to sell any stock to the holder as the value will not appreciate.