An estrogen blocking drug Tamoxifen used to treat breast cancers is believed to have osteoporosis as a side effect. To test this concern, cancer subjects (women with cancer) were randomly selected and given Tamoxifen and their bone density was recorded before and after the course of the treatment.

Question: Is this is a completely randomized experiment? True or False and explain thoroughly

Also can you explain to me what exactly is a "completely randomized experiment" vs just a normal randomized experiment, or are they equivalent?