Answer: option b
Step-by-step explanation: In simple words, collinearity refers to the condition under which some of the Independent variables in the model are related to each other. This international between independents variables can result into incorrect results while fitting the model.
Therefore, collinearity causes problem as the analyst prepares a model on the basis that there will be two inputs one is dependent another is independent but due to this phenomenon the expected input structure collides.
Hence from the above we can conclude that the economist should be concerned with col linearity.