The narrow tube AC forms a quarter circles in a vertical plane. A ball B has an area of cross-section slighly smaller than that of the tube and can move without friction through it. B is placed at A and displaced slightly. During the motion from A to C it will :

A. Always be in contact with the inner wall of the tube
B. Always be in contact with the outer wall of the tube
C. Initially be in contact with the inner wall and later with the outer wall
D. Initially be in contact with the outer wall and later with the inner wall.