Explanation:

- The Sultan Azlan Shah Cup is an annual international men's field hockey tournament.

- It is named after Sultan Azlan Shah, a former Malaysian King and a big supporter of field hockey.

- The tournament usually takes place in Ipoh, Malaysia.

- Option 1: Malaysia - This is the correct country that hosted the 2019 Sultan Azlan Shah Cup hockey tournament.

- Option 2: Singapore - Singapore has not hosted the Sultan Azlan Shah Cup.

- Option 3: India - India is a regular participant but has not hosted the tournament.

- Option 4: China - China has not hosted this particular event.