Question

how many test groups does an experiment have?
none
only 1
1 or more
always 2

Explanation:

In an experiment, there can be one or more test groups. A test group is a group that receives the treatment or intervention being studied. Sometimes, there may be multiple test groups with different levels or types of the treatment. For example, in a drug - testing experiment, there could be a group receiving a low dose of the drug (test group 1), a group receiving a high dose (test group 2), etc.

Answer:

1 or more