Which of the following countries co-sponsors the annual multilateral military exercise "Cobra Gold" along with Thailand?

Introduction / Context:
Cobra Gold is one of the largest and longest running multilateral military exercises in the Asia Pacific region. It is regularly mentioned in defence news and international relations discussions. Many competitive examinations include questions on important military exercises and their participating countries, so it is useful to know who co-sponsors Cobra Gold with Thailand.

Given Data / Assumptions:
- The exercise named in the question is Cobra Gold.
- Thailand is already mentioned in the question as one of the organisers.
- The options list India, Indonesia, the United States of America, China and Japan as possible co-sponsors.

Concept / Approach:
Cobra Gold is closely linked with defence cooperation between Thailand and the United States, and it has grown into a major multilateral exercise involving several regional partners and observers. The key concept here is to identify the long term principal partner of Thailand in organising this exercise. Recognising that the United States is heavily involved in Asia Pacific defence exercises allows us to choose the correct option confidently.

Step-by-Step Solution:
Step 1: Recall that Cobra Gold is conducted in Thailand and is primarily associated with the Thai and United States armed forces. Step 2: Examine the options. India, Indonesia, China and Japan may participate in various regional exercises, but they are not traditionally recognised as co-sponsors of Cobra Gold. Step 3: Note that the United States has a long standing defence partnership with Thailand and plays a central role in this exercise. Step 4: Use this knowledge to identify the United States of America as the correct co-sponsoring country. Step 5: Confirm that no other option fits the specific co-sponsor role as accurately as the United States.

Verification / Alternative check:
Reports on defence cooperation in the region consistently describe Cobra Gold as a joint Thai United States exercise that later expanded to include multiple nations. Official communication from the United States Department of Defense and Thai military sources list both countries as key organisers. This cross checking confirms that the United States is the co-sponsor mentioned in the question.

Why Other Options Are Wrong:
India: India participates in other exercises such as Malabar and has joined some editions of Cobra Gold, but it is not a co-sponsor of the exercise.
Indonesia: This country may take part in regional drills but does not co-sponsor Cobra Gold with Thailand.
China: It is not the long term co-organiser of Cobra Gold and has had a different pattern of participation and relations in the region.
Japan: While Japan is involved in several joint exercises, it does not act as the primary co-sponsor for Cobra Gold.

Common Pitfalls:
A frequent error is to confuse participation with sponsorship. Many countries join multinational exercises as participants or observers, but that does not make them co-organisers. Another pitfall is mixing up various Asia Pacific exercises, such as Malabar, RIMPAC and others, and assigning the wrong partner country to the wrong exercise. Keeping a small list of key exercises and their main organisers helps avoid this confusion.

Final Answer:
The country that co-sponsors the multilateral military exercise Cobra Gold along with Thailand is the United States of America.