I just took an EasyMandarin test, and one of the questions is:
The possible candidates to fill in the blank is: 了，去，过，and 到.
I picked up 了 but the correct answer was 到.
Now, according to this answer, the difference between 到 and 了 is:
了 and 到/著(着) (zháo) serve different functions in sentences.
了 used after verbs implies a sense of "stopped, finished,completed, or done" on the action.
到 and 著(着) used after verbs indicate the result of the action.
But then why is 到 correct here? It seems to me that the sentence is "Did you purchase a flight ticket?", which is a completed action, so it seems 了 is correct.
Why is 到 the correct answer and what is the meaning of the sentence?
Hmmm... I still don't get it. It seems that 买得到 as a phrase functions as a verb (but 买得了 not). So in this sentence is 得 not considered a degree complement?