Final answer:
The terms 'upstream' and 'downstream' in a supply chain can have multiple meanings, and both options a and b are correct.
Step-by-step explanation:
The correct statement is d) Both a and b.
In a supply chain, the term 'upstream' refers to a member sending output to another member, while 'downstream' refers to a member using the output as input.
So, option a is correct.
A single member of a supply chain can be both upstream and downstream from one or more members.
For example, a manufacturer may be upstream to its suppliers and downstream to its customers.
Therefore, option b is also correct.