These recent initiatives owe a great deal to one artist, Peter Senior, who set up his studio at a Manchester hospital in north-eastern England.
The quality of the environment may reduce the need for expensive drugs when a patient is recovering form. an illness. A study has shown that patients who had a view on to a garden needed half the number of strong pain killers compared with patients who had no view at all or only a brick wall to look at during the early 1970s. he felt the artist had lost his place in modern society, and that art should be enjoyed by a wider audience.
A typical hospital waiting room might have as many as 5 000 visitors each week. What better place to hold regular exhibitions of art？ Senior held the first exhibition of his own paintings in the out-patients' waiting area of the Manchester royal Infirmary in 1975. Believed to be Britain's first hospital-artist, Senior was so much in demand that he was soon joined by a team of six young art school graduates.
The effect is striking. Instead of the familiar long, barren corridors and dull waiting rooms, the visitors experience a full view of fresh colours, playful images and restful courtyards.
Compared with the total number of Britain's National Health Service hospitals, the hospitals which have art collections is only ______.

A. 4%
B. 40%
C. 25%
D. 50%.