The correct answer is: C. Either I or II is strong
Argument I is strong because it is based on a valid reason. Creating job opportunities is a good reason to start new big industries in Mumbai.
Argument II is weak because it is based on an assumption. It assumes that new big industries will further add to the pollution of the city. However, this assumption is not necessarily true. New big industries could be started in Mumbai in a way that does not add to the pollution of the city.
Therefore, either argument I or argument II is strong.