The correct answer is option 1: Quotas. Quotas are a type of non-tariff trade barrier that limit the quantity of goods that can be imported or exported. This restriction is set by the government and aims to protect domestic industries by limiting foreign competition.

Option 2, Health regulations, refers to regulations and standards related to the safety and quality of products in order to protect public health. While health regulations can be a trade barrier in some cases, they are not considered the most important type of non-tariff barrier.

Option 3, Pollution standards, refers to regulations and standards aimed at preventing pollution and protecting the environment. While these can also be trade barriers in some cases, they are not considered the most important.

Option 4, Labelling and packaging regulations, refers to regulations related to how products are labeled and packaged. While these regulations can have an impact on trade, they are not considered the most important non-tariff barrier.

In summary, while the other options can also be non-tariff trade barriers, quotas are generally considered the most important type.