Which sentence in each group is correct? Are they both acceptable?
I can't tell if you are joking or being serious.
I can't tell if you are joking or if you are being serious.
Is it better to regret believing in someone's lie or doubting someone's truth?
Is it better to regret believing in someone's lie or to regret doubting someone's truth?
I have been browsing through various related threads in order to clear up the issue, but for some reason I keep thinking that the first sentence in each group doesn't sound quite right. A friend of mine claims they are both correct in each case and that the first sentences are preferred for brevity. Is he right?