Which of the following accurately describes the taxation of sole proprietorships and freelancers?

a$)$ Sole proprietorships and freelancers are taxed at corporate tax rates.

b$)$ Sole proprietorships and freelancers are not subject to income taxation.

c$)$ Sole proprietorships and freelancers are taxed at individual tax rates.

d$)$ Sole proprietorships and freelancers are taxed at a fixed rate regardless of income levels.