Select the correct algebraic expression.

Solving form the option;

option(a)  ab - a -b+1 = (a - 1) (b - 1)

              ab - a - b +1 = ab - a - b +1 this is correct 

Option (b) 
​ab + a – b + 1 = (1 – a) (1 – b) (1 – a) (1 + b) 

ab + a - b + 1 =$$1−2a+a^2−b^2+2ab^2−a^2b^2$$, this is not correct.

Option(c) 

​ab – a – b + 1 = (1 – a) (b – 1) 

ab - a -b + 1 = b - 1 - ab + a, this is also not correct. 

Option (d), 

 ab – a – b + 1 = (a – 1) (1 – b) 

ab - a - b + 1 = a - ab - 1 + b this is not correct.

from the above, we can see that only option (a) is correct.

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