You will be given a definition of a task first, then some input of the task.
This task is about reading the given passage and construct a question about the information present in the passage. Construct a question in such a way that (i) it is unambiguous, (ii) it is answerable from the passage, (iii) its answer is unique (iv) its answer is a continuous text span from the paragraph. Avoid creating questions that (i) can be answered correctly without actually understanding the paragraph and (ii) uses same words or phrases given in the passage.

Estonia co-operates with Latvia and Lithuania in several trilateral Baltic defence co-operation initiatives, including Baltic Battalion (BALTBAT), Baltic Naval Squadron (BALTRON), Baltic Air Surveillance Network (BALTNET) and joint military educational institutions such as the Baltic Defence College in Tartu. Future co-operation will include sharing of national infrastructures for training purposes and specialisation of training areas (BALTTRAIN) and collective formation of battalion-sized contingents for use in the NATO rapid-response force. In January 2011 the Baltic states were invited to join NORDEFCO, the defence framework of the Nordic countries.
Output:
Which countries aid Estonia in trilateral defense strategies?