Refer to figure. 
Here are the main properties of the gyroscopic instruments you need to know:

This is a question where it is easiest to work out which axis is “missing”, as the “missing” axis is the one that the instrument is measuring. Because of gyroscopic precession, the axis that the gyro cannot turn about is actually the one being measured by the gyro's turn about a different axis (never the spin axis though, of course). These are therefore “rate” gyros, using precession to measure the movement about a single axis, usually against a spring.

• Gyro A – The spin axis is horizontal (pitch axis), and the gyro can move about the roll axis. Since there’s no degree of freedom around the yaw axis, it is a yaw gyro. This is the exact setup of a turn indicator.
• Gyro B – The spin axis is vertical (yaw axis), and the gyro can move about the pitch axis. Since there’s no degree of freedom around the roll axis, it is a roll gyro.
• Gyro C – The spin axis also vertical (yaw axis), but the gyro cannot move about the pitch axis, only about the roll axis. Therefore, it is a pitch gyro.