For a yes/no question, "whether" is preferred. That's the rule I was taught, anyway.
I agree that "whether" should be accepted here
Why is "if he plays" not accepted? Does "leger" not translate as "plays" and "playing"?
June 22, 2018: whether was accepted
"Whether" and "if" should both be acceptable responses for om han leger med katten.
"If he plays with the cat" was rejected by the program and should be a correct answer along with "if he is playing with the cat".
why was there no question mark to signify a question ?