A compass needle of oscillation magnetometer oscillates 20 times per minute at a place P of dip 30°. The number of oscillations per minute become 10 at another place Q of 60° dip. The ratio of the total magnetic field at the two places (BQ : BP) is:
(A) √3 : 4
(B) 4 : √3
(C) √3 : 2
(D) 2 : √3
