How can Helen provide free delivery for a small group of promotional products?

Q) How can Helen provide free delivery for a small group of promotional products?

a) Set the default delivery for all products to a flat rate of £0.00
b) Add “Free delivery” to the Shopping campaign promotional text
c) Remove all delivery options from the Google Merchant Center account

d) Update the ‘delivery’ attribute to a fixed delivery price of £0.00 for only the promotional products