Answer:
3. a purchase order.
Explanation:
Normally, the buyer's offer in a commercial transaction takes the form of a purchase order. Commercial transaction refers to the law guiding, regulating or governing business transactions and deals.
A purchase order can be defined as an official document which a buyer send to sellers of goods and services in order to document and have a record of the sale of products and services to be delivered to the buyer at a later date. It allows making order without paying immediately.