If I have various investment projects relating to the development of resources, methane hydrate buiness will not be in my choices. The purpose of the investment is to make money in the short-term future. In that points, methane hydrate has many constraints. First, the technology of mining the methane hydrate and manufacturing gas was not verified commercially. Second, the mining cost is higher than the selling price, so its profitability is low. Third, there are so many alternatives such as solar energy, nuclear energy, shale-gas, etc

However, methane hydrate has potential to play an important role in the alternative energy resources. Therefore, the USA and developed countries should do R&D activities in order to develop the technology of exploiting the methane hydrate.

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1) Methane hydrate is uncountable. Liquids and gasses are uncountable. Therefore, it's singular. "methane hydrate has many constraints".
--You did do this correctly further down in "methane hydrate has potential,,,"

2) Because it's uncountable, it's rarely definite (the methane hydrate) unless we're talking about a specific gas
--> "The methane hydrate of Japan" for example

Not bad at all!! Minimal corrections :) Nice job!