Answer: 3. It would discourage trade
Step-by-step explanation:
An infant industry is one that just recently started and as such neither has the scale nor the expertise for the market it is in, at least not yet. For this reason their prices may be relatively high as they have not achieved economies or scale or rather they are not able to charge lower prices as they can only produce relatively fewer goods and haven't learnt proper cost effective methods.
Introducing tariffs will reduce trade from outside with more established companies in the market who would be able to charge lower prices thereby killing the infant industry. By applying tariffs, the price of goods from the more established companies will at least be on par or more expensive than normal thus making the market more competitive which will be good for the infant industry.