A transformer consists of two loops of wire with an AC current going through the "primary" loop inducing a voltage, and therefore a current, in the "secondary" loop.
The ratio of the induced voltage in the secondary loop to the voltage in the primary loop is equal to the ratio of the number of turns in the secondary loop to the number of turns in the primary loop.
A step-up transformer is designed to make the induced voltage in the secondary loop greater than the voltage in the primary loop. This requires the primary loop to have fewer turns than the secondary loop.
Choice C