Question 8 and the verb 'trabajar'

Question

For Question 8   I answered 'trabaje' believing it to be the correct subjunctive form but it was marked incorrect and 'trabaja' was given as the correct answer.  Would you please explain.  Many thanks.

Accepted Answer

Hola Trefor
This is the test-question you came across:
 
Ella va de compras con su hija mientras Alfredo ___ en el garaje.
She goes shopping with her daughter while Alfredo works in the garage.
You need the indicative here "trabaja" because it is expressing two simultaneous actions. If we had said "as long as..." (with a conditional meaning), then you would have needed the subjunctive "trabaje". 
I hope it clarified it.
Saludos

Answer

Thank you Inma. I understand it now.