39. Linda uses a Michelson interferometer with the 606-nm light from a krypton-86 lamp and she places a gas cell of length 10.0 cm in the arm of movable mirror (as shown in the figure). Assuming the cell is filled with air at 1 atm which has an index of refraction n = 1.00025. Find the number of fringes moving across a line in her field of view if Linda slowly pumps out the air in the cell.

(A) 413
(B) 41.3
(C) 165
(D) 16.5
(E) none of the above.