Trade can be described as

Trade is the exchange of goods and services for money or for other goods and services. At its core, trade involves two sides of a transaction meeting: someone selling and someone buying. This buying-and-selling activity is what links producers to consumers and allows goods to move from where they are made to where they are wanted.

The other options each describe only part of the wider commercial process. Distribution of goods refers to the physical movement and spreading of goods to different locations, which is a service that supports trade rather than trade itself. Purchase of goods and services covers only the buying side of a transaction, leaving out selling. Production of goods is the making of goods and services, which happens before trade takes place and is a separate economic activity.

Examination reminder: trade is always a two-sided activity; whenever an option names only one side (buying alone, or moving goods alone), it cannot be the full definition of trade.