whose room is this?--__________a ,the twins' b.the twin's

答案：A the twins‘
此题可以直接转换为一句：This is the twins' room.
the twins是指两人,且词尾以s结尾,所以其所有格形式只需要加',表示“双胞胎同住的”即可.
the twin貌似不会单独使用,一般会说成the twins,the twin brother(s)/sister(s).