Step 1: The stem asks for the current label applied to Down syndrome, a chromosome 21 trisomy with intellectual disability in the mild-to-moderate range.
Step 2: This is a flawed question because no option is a genuine present-day equivalent of Down syndrome; the recall answer key records option (a).
Step 3: Working through the alternatives - oligophrenia is a dated umbrella word for low intelligence, while madness and mentally unstable are non-clinical, derogatory expressions, so they are easily discarded.
Step 4: Per the printed key the chosen response is option (a).
\[\boxed{\text{Option (a)}}\]