Which of the Following Statements Concerning Structural Isomers Is/are Correct

Multiple Choice

Which of the following statements concerning structural isomers is/are correct?
1) Structural isomers have the same elemental composition,but the atoms are linked in different ways.
2) Structural isomers have identical physical properties,but different chemical properties.
3) Structural isomers have identical structures,but contain different isotopes of the same elements.

A) 1 only
B) 2 only
C) 3 only
D) 1 and 2
E) 1,2,and 3