Should "the" and "a" agree in the same sentence?
Example:
She lowered her pen to the blank page and wrote the first verse—followed by a second one.
In this case, I used the first and then a at the end. Is this grammatically correct?
Perfectly correct. Otherwise how would you say:
'I went to THE World Cup in Brazil in AN aeroplane'?
You would either have to say 'a World Cup', or 'the aeroplane', both of which would be nonsense.