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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) = + 5x + 4
b) (x+2)(x+2) = + 4x + 4
c) (x+5)(x-1) =  + 4x - 5
d) (x+2)² = + 4x + 4

Items b and d are the same ⇒ Square of Binomial that yields a product called Perfect Square Trinomial.