(二)請詳細說明形成死結(Deadlock)的原因，並且說明應該如何防止死結？(5 分)

1. A couple has the same chance to give birth to a boy and a girl, and decides to have 3 children. If none of the 3 is a girl, they will try again; and if they still don't get a girl, they will try once more. If the random variable \( X \) denotes the number of children the couple will have following this scheme, then what is the expected value of \( X \)? (1)