Correct Option: C

sanatorium (N.) : a place like a hospital where patients who have a lasting illness or who are getting better after an illness are treated
hospital (N.) : a large building where people who are ill/sick/ injured are given medical treatment and care
asylum (N.) : a hospital where people who were mentally ill could be cared for, often for a long time
retreat (V.) : to move away from a place ; to recede ; to back off ; to retire