Read the following passage and fill in each gap with a suitable word based on the information of the passage:

Scientists have identified Hydrogen as another form of renewable energy source. It is the most abundant element in nature. But it does not exist seperately as a gas. It is always combined with other elements, such as with Oxygen to make water. Hydrogen, separated from another element, can be burned as a fuel to produce electricity.

Scientists have (a)____ out that Hydrogen can be (b)____ as renewable energy source. The nature is (c)____ with Hydrogen  (d)____ it does not exist separately as gas. Hydrogen and Oxygen (e)____ water.