阅读文章，根据文章内容，完成表格，一空一词

　　你身边有双胞胎同学吗？他们的举止、行为你好奇吗？你对他们有研究吗？认真阅读下面的文章，你会对双胞胎有新的认识！

　　There are two types of twins： identical(相同的)and non－identical twins．Identical twins are formed from a single egg in mother's body which divides to form two separated(分开的)babies．Identical twins look the same, and are often dressed by the parents in clothes of the same colors．It is often difficult to tell identical twins from each other, even when they are standing side by side．Non－identical twins came into being when the mother produces two separated eggs at the same time, both of which grow to from babies．In the case the twins look like normal brothers and sisters and easy to tell one from the other．

　　In the 1970s and 1980s a scientist did some research into twins．He invited many pairs of identical twins to university and asked them to take part in a week of tests．He was particularly interested in adopted(领养)twins who had been separated, at birth．He would give the twins different kinds of tests to study their speed of thinking, their speech, their memory, the ways they saw and heard different things, and so on．Time and time again he found separated twins who preferred clothes of the same colors, used the same kind of shaving soap, wore the same shaped square glasses and the same colored socks．

　　There is a third type of twins, but it is a very unusual one．Twins who are joined together at birth are known in western countries as Siamese(连体)twins．