it's a toss-upspokenUNCERTAIN used when you do not know which of two things will happen, or which of two things to choose 这事尚难预料,这事尚未定夺 I don’t know who’ll get the job – it’s a toss-up between Carl and Steve. 我不知道谁会得到这份工作——卡尔和史蒂夫都有可能。
→ it’s a toss-up at toss-up(1)