The correct answer is A. shorten.
A tonic is a liquid preparation that is taken or applied to the body to improve health or appearance. In the context of hair, a tonic can be used to strengthen, condition, or add shine to hair. It can also be used to prevent hair loss or to promote hair growth.
The word “vitalize” means to give life or energy to something. In the context of hair, a tonic that vitalizes hair would make it look and feel healthier and more vibrant.
The word “shorten” means to make something shorter. In the context of hair, a tonic that shortens hair would make it look shorter. However, this is not the intended effect of a tonic.
The word “enfeeble” means to make something weak or feeble. In the context of hair, a tonic that enfeebles hair would make it look and feel weak and unhealthy. However, this is not the intended effect of a tonic.
The word “repress” means to hold back or suppress something. In the context of hair, a tonic that represses hair would make it look and feel flat and lifeless. However, this is not the intended effect of a tonic.
The word “clamour” means to make a loud, continuous noise. In the context of hair, a tonic that clamoured would make a lot of noise when it was applied. However, this is not the intended effect of a tonic.