The third movement of the sonata form is referred to as the
a. recapitulaton.
b. variation.
c. finale.
d. cadenza

The third movement of the sonata form is referred to as the as the Cadenza.

So, Option D is correct which is cadenza.

The structure of Sonata form is based on contrasting of musical ideas, consisting of three main sections: exposition, development, and recapitulation and sometimes there is a fourth section which is also included that is Coda. There are four movements in Sonata form.

i think it is organic art