Benzene (C6H6) is a cyclic compound consisting of six carbon atoms and six hydrogen atoms. It is a highly stable molecule that exhibits unique properties due to its delocalized pi-electron system. Let's analyze each statement about benzene and determine the correct ones.

a) (C=C) bond is shorter than (CC) bond:
This statement is incorrect. In benzene, all carbon-carbon (C-C) bonds have the same length. The bond length is approximately 1.39 Å, which is intermediate between the typical single bond (1.54 Å) and double bond (1.34 Å) lengths. The bond lengths in benzene are equal due to the delocalization of pi-electrons in the aromatic ring.

b) All (C H) bonds are equivalent:
This statement is correct. In benzene, all carbon-hydrogen (C-H) bonds are equivalent. This means that each hydrogen atom is bonded to a carbon atom in the same environment, experiencing the same electronic and steric effects. The equivalent C-H bonds contribute to the symmetry and stability of the benzene molecule.

c) C-atom is sp2-hybridized:
This statement is correct. In benzene, each carbon atom is sp2-hybridized. The carbon atom forms three sigma bonds, with two of them forming a double bond with adjacent carbon atoms and the third bond being a sigma bond with a hydrogen atom. The trigonal planar geometry around each carbon atom is a result of sp2 hybridization.

d) All (C=C) and (CC) bonds are of equal stability:
This statement is correct. In benzene, all carbon-carbon (C=C) and (CC) bonds are of equal stability. This is due to the delocalization of pi-electrons in the aromatic ring, which creates a resonance structure with alternating single and double bonds. The resonance stabilization energy makes all the bonds in benzene equally stable.

In summary, the correct statements about benzene are:
- All (C H) bonds are equivalent.
- C-atom is sp2-hybridized.
- All (C=C) and (CC) bonds are of equal stability.