If you mean full product, none of items a) to d) yields a complete product of x² only.
If you mean the first term or leading term of the product is x², all the products of the items a) to d) have x² as the first or leading term of their products.
a) (x +1)(x+4) = x² + 5x + 4
b) (x+2)(x+2) = x² + 4x + 4
c) (x+5)(x-1) = x² + 4x - 5
d) (x+2)² = x² + 4x + 4
Items b and d are the same ⇒ Square of Binomial that yields a product called Perfect Square Trinomial.