The correct answer is: C. Either I or II is strong.
Argument I is strong because it is based on the fact that the customer has to pay less when they buy things on instalments. This is because they are not paying the full price of the item upfront, but are instead paying it off in smaller amounts over time. This can be a good option for people who cannot afford to pay the full price of an item upfront, or who would prefer to spread out the cost over time.
Argument II is weak because it is based on the assumption that paying instalments upsets the family budget. This may be true for some families, but it is not necessarily true for all families. Some families may be able to manage their finances well enough to pay instalments without upsetting their budget.
Therefore, either argument I or argument II could be strong, depending on the specific circumstances of the customer.