full infinitive or bare infinitive

[chance22]

In the following sentence: The duty of a doctor is to treat the sick, cure the injured, and to save lives.
1. Can I omit the second "to"? That is: The duty of a doctor is to treat the sick, cure the injured, and save lives.
2. Is it also OK for me to use full infinitive for all the phrases here? That is to say: The duty of a doctor is to treat the sick, to cure the injured, and to save lives.
I just lack the language sense here, so could you explain it to me? Thank you.

[emsr2d2]

In the following sentence: The duty of a doctor is to treat the sick, cure the injured, and to save lives.
1. Can I omit the second "to"? That is: The duty of a doctor is to treat the sick, cure the injured, and save lives.
2. Is it also OK for me to use full infinitive for all the phrases here? That is to say: The duty of a doctor is to treat the sick, to cure the injured, and to save lives.
I just lack the language sense here, so could you explain it to me? Thank you.

As far as general English usage is concerned, both versions are regularly used, understood and I would say, are both fine.

[Raymott]

I agree, but I'd add that if you're going to use "to" for the last phrase, you should also use it for the second (for all).

to A, to B, and to C. or: to A, B, and C. but not: to A, B, and to C.

[chance22]

Ok I got it. Thank Raymott and emsr2d2 very much.