Answer: $\mathbf C$
Explanation:
$\because$ pizza cannot be ordered without any topping and pizza can be ordered with at most 3 toppings.
So, only $3$ possibilities are there $$= 6C_1 + 6C_2 + 6C_3$$
$$ = 6 + 15 + 20$$
$$ = 41$$
$\therefore \mathbf C$ is the correct option.