agrasan
I am not clear how the answer to this question is
(B), I think it should be (E) only as we are not given anything on
correlation whether it's positive or negative. Could you please help me if I am missing anything critical in the language?
As many have said before,
the answer as it is currently written would be E if a real GMAT test writer had written it. If the GMAT wants you to know the direction of the relationship, they WILL tell you explicitly (directly proportional, positively correlated, etc). Absent that language, a "linear relationship" can have a positive, negative OR 0 slope.
A linear relationship is defined as the following: A = mF + b (where F=forecasted units, A = actual units, m=slope of the line, and b a constant for the y-intercept).
So let's imagine a few scenarios, like a slope of 1, 0, and -1 (for ease). You can choose whatever constant you want, but I let the constant in the positive slope case just be 0, while setting it to anything for the 0-slope case just so that the entries don't disappear to 0. For the negative slope, we just need to set B to something large enough to keep units sold positive, but we just need to pick something big, so maybe 40?
The table below shows the Forecasted and then actuals under each case:

In the case of a positive slope, YES, April Actual is greater than March actual. However, in the case of a 0 slope or a negative slope, they are either equal or reversed. Therefore, it cannot be known whether actual April was greater than Actual March.

Whit