A, B, C, or D?

The answer: D

Refer to the figure below.
In each option, the carbon atom on each side with higher priority is circled blue.

For A and B:
The two groups of higher priority are on the opposite side of the C=C double bond. Each alkene has E-configuration.

For C:
Two methyl groups are attached to the left carbon atom of the C=C double bond. There is no geometrical isomerism. Hence, there is no E-configuration or Z-configuration.

For D:
The two groups of higher priority are on the same side of the C=C double bond. The alkene has Z-configuration.

The last one, D