all we could do was changing (OR change, to change) our tickets

[Adil]

Privet!

What is the correct option:

1) all we could do was changing our tickets
2) all we could do was change our tickets
3) all we could do was to change our tickets

I think 1) and 2) are correct. What do you think?

Thanks in advance.

[PERPETRATOR™]

Двоечник...

[great cat]

PERPETRATOR™ +1

[Monday]

to change

[segu]

Advanced Grammar in Use (Hewings) и Grammar and Vocabulary for Cambridge Advanced and Proficiency допускают 2 варианта в такой конструкции:

2) all we could do was change our tickets
3) all we could do was to change our tickets

Например
What he did was (to) sell his flat...
или
All we are going to do is take your teeth out.