$A, B$ and $C$ are three non-empty sets. If $A \subset B$ and $B \subset C$, then which of the following is true?
(1) $\mathrm{B}-\mathrm{A}=\mathrm{C}-\mathrm{B}$
(2) $A \cap B \cap C=B$
(3) $\mathrm{A} \cup \mathrm{B}=\mathrm{B} \cap \mathrm{C}$
(4) $A \cup B \cup C=A$