Which of the following distinguishes an observational study from a randomized experiment?

In an observational study volunteers are always used, whereas in a randomized experiment a random sample is always taken from the population.

In an observational study a random sample is always taken from the population, whereas in a randomized experiment volunteers are always used.

In an observational study treatments are not randomly assigned, whereas in a randomized experiment treatments are randomly assigned.

In an observational study a control group is never used, whereas in a randomized experiment a control group is always used.