How do we use Conditional II in English?

[Bruno]

Test No. incompl/elem-11 "Conditionals", question 6

I will try very hard to come and have dinner at your house if I ......... able to.

(a) am
(b) was
(c) were

Test No. incompl/elem-11 "Conditionals", answer 6

I will try very hard to come and have dinner at your house if I am able to.

Correct answer: (a) am

Your answer was: incorrect
I will try very hard to come and have dinner at your house if I were able to.
_________________________

This is a matter of "main clause (future tense) and if clause (present tense), isn't it?

[Mister Micawber]

.
Yes, it is.

I will come if I can.
If he goes, I will go too.

vs

I would come if I could.
If he went, I would go too.
_________________
Canadian-American native speaker
who teaches English for a living at Mister Micawber's
ESL cafe: Interview with Mister Micawber