Buoys dropped in lake 
Seven buoys A, B, C, D, E, F, and G are released in a lake at regular intervals in a manner to make a square pattern as shown in the figure. The buoys A, C, E, and G are on the vertices and the buoys B, D, and F are midpoints of sides of the square. If the buoys were released in a uniformly flowing river in the same manner, the buoy G falls on A. What pattern would they make in the river?

options: 

I and my friends thought of the problem for a long, and found that these were the obstacles which were keeping us from the solution

*

*What can we infer from the statement that " the buoys are released into lake at regular intervals"?

*If the river is uniform, then how do they fall on each other? we figured out it's something related to time delay but can't pinpoint it.

*Since the figure is square, would the buoys be dropped at different places? If they were dropped at the same place, then it's impossible that they can flow to different directions since the river is said to be uniform.

*Since CDE doesn't seem to change in any options, it can be inferred that the velocity field of the river is in the horizontal direction

The correct answer is (d) but not sure how to arrive at it.
 A: To summarize the discussion in the comments:
The problem is very poorly worded, but we can reverse engineer a sensible interpretation, using the official answer.
Interpretation:  The drop points are indicated by the initial square, of sidelength $S$ (let's say).  These never change.  They represent the points at which the various buoys will be dropped, in alphabetical order, one after the other.  At time $1$ $A$ is dropped, at time $2$ $B$ is dropped, down to time $7$ at which $G$ is dropped.  Thus $A$, for example, has drifted for $6$ time intervals by the time you drop $G$.  The phrase "$G$ falls on $A$" means that, by the time you drop $G$, $A$ has drifted to $G$'s drop point.  Thus, each buoy travels $S$ units in $6$ units.
Using this interpretation, $d$ is the only possible answer since it is the only one in which $E,F$ are downstream from $G$.  Indeed, we can explain each point in the figure given by $d$.  Take $D$ for instance.  $D's$ drop points is at the midpoint of a square.  And $D$ drifts for $3$ time intervals, hence it drifts $\frac S2$ which means it should have moved to $E's$ drop point, on the side with $G$.  Indeed, in the figure $d$ the buoy $D$ winds up parallel to $G$, as it should.
