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Identifying a Diene

The four isomeric C9H14 dienes listed below all give 1,1-dimethylcycloheptane on exhaustive catalytic hydrogenation.

A 5,5-dimethyl-1,3-cycloheptadiene
B 6,6-dimethyl-1,3-cycloheptadiene
C 6,6-dimethyl-1,4-cycloheptadiene
D 3,3-dimethyl-1,4-cycloheptadiene

Because of their symmetry, two of these isomers have five structurally distinct carbon atoms; the other two have eight such carbons.
One of the symmetrical dienes (X) has a uv absorption maximum near 250 nm.
The other symmetrical diene (Y) does not absorb uv light above 200 nm in wavelength.

1. Which isomer is X? A B C D
2. Which isomer is Y? A B C D


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