Select the most appropriate option to fill in the blank.

The government has warned the traders not to ______ onions.

hoard

The correct option to fill in the blank is hoard.

The word "hoard" means to collect and store something away, especially in a secret or excessive way. It is the most appropriate word to use in this context, as it conveys the meaning of the traders being warned not to buy and store onions in large quantities in order to create an artificial shortage and raise prices.

The other options are not as appropriate.

• Gross means unpleasantly large or excessive. This is not the right word to use, as it does not convey the same meaning as "hoard."
• Combine means to join two or more things together to form a single unit. This is not the right word to use, as it does not make sense to say that the traders are combining onions.
• Bulk means a large quantity of something. This is not the right word to use, as it does not convey the same meaning as "hoard."