Two conjugations?

Question

In the question, Yo ________ llegado pronto a trabajar esta tarde, why is llegar conjugated? I thought if the first verb ( in the blank is the conjugated form of  haber) is conjugated the second verb is left in the infinitive form.

Accepted Answer

Hola Mollie
The auxiliary verb haber is used to form the present perfect tense of other verbs, i.e. to say I have gone, you have done, he has worked, etc.. 
The first part of the present perfect structure is the verb haber in the present, as in saying: I have..., you have..., he has... and then the second part is the main verb in the past participle form: ido, trabajado, tenido...etc. Here, in this lesson we are only testing the first part of the verbal structure, the part with haber: he, has, ha, hemos, habéis, han. 
So here in this sentence you need:
Yo he llegado pronto a trabajar esta tarde.
I hope this clarified it.
Saludos
Inma

Answer

Yo hay llegado pronto a trabajar esta tarde