They are identical twins and it's impossible to tell them apart.他们是同卵双胞胎，根本分不出谁是谁。He couldn't tell the difference between plonk and a decent bottle of wine.他分不出劣等葡萄酒和上等葡萄酒有什么差别。They look rather alike and you don't know at first which is which.他们看上去很相像，猛一看你都分不出谁是谁。