The selection of 'd' may be based on the following somewhat odd logic.
The calculated minimum is LDR * 1.15 * 1.15 * 1.43 = LDR*1.891175.
Of the four choices presented, the only one which meets the required minimum is (d). So if you had to choose one of those four multipliers, you'd have to go with 1.97, because 1.87 is below the required minimum.
I think it's a stupid logic trap if they intended that, because the question is poorly worded also. But that might be thought process involved....