Answer:
Option B, two variables are measured and two groups are compared
Step-by-step explanation:
In a correlation study relationship between two variable is established.
The two variables represents two group.
For instance correlation study is conducted to determine the relationship between two variables X and Y
X and Y are variable
While X represents the group "number of cars passing through a lane"
Y represents the group "width of the road".
Hence, Option B is correct
