Select all polynomials that factor into a product into two binomials.
a)       25m² – 9n²
b)      25m² – 30mn + 9n²
c)       25m² – 30mn – 9n²
d)      25m² + 30mn + 9n²
e)      25m² + 9n²

The correct answer is: a), b), d)

Here, we have to find the polynomials that can be factorised into two linear polynomials.
We have, 25m² – 9n² = (5m)² – (3n)² = (5m – 3n) (5m + 3n)
25m² – 30mn + 9n² = (5m)² – 2(5m) (3n) + (3n)² = (5m – 3n)² = (5m – 3n) (5m – 3n)
25m² + 30mn + 9n² = (5m)² + 2(5m) (3n) + (3n)² = (5m + 3n)² = (5m + 3n) (5m + 3n).
The other two polynomials cannot be factorised.
Hence, the correct option is C.

Factorisation is breaking down of a polynomial into polynomials of lesser degrees.