Concept:Invisible trade refers to the import and export of services rather than physical goods.
Explanation:A favourable invisible trade account occurs when the value of services exported is higher than the value of services imported.
Developing tourism and other services attracts foreign visitors and increases service earnings.
This raises the export of services and improves the invisible trade account.
Imposing high tariffs on exports relates to visible goods, not services, and may discourage trade.
Encouraging people to seek medical treatment abroad increases service imports, which worsens the account.
Increasing the export of primary products is part of visible trade, not invisible trade.
Thus, promoting tourism and other services is the correct method.
Answer:A. developing tourism and other services.