The contraction of muscle is leading to “spasm”. This spasm is referred as the tonic nature of that particular part.
The other words such as “decrease or moderate” are representing degree of spasm but they do not represent the cause.
Thus, the options (c), (d) and (b) are incorrect.
The contraction of muscle is leading to “spasm”. This spasm is referred as the tonic nature of that particular part.
Therefore, the correct option is – A. spasm.