Answer:
1. a. that water aids digestion is really true.
2. e. subject
Explanation:
A noun clause is a group of related words with at least a subject and a verb that that does not express a complete thought on its own and that functions as a noun in a sentence, thus, it can function as a subject, object, predicate noun, or others. We can also identify this type of clause because it normally begins with the words <em>that, what, whatever, whether, when, where, who, whom, whoever, which, whichever </em>or<em> why.</em>
In this case, the sentence that uses a noun clause to combine the two ideas is <em>a. that water aids digestion is really true</em>. “That water aid digestion” is the noun clause because it has both a subject and a verb (<em>water</em> and <em>aid</em>), it begins with “that,” and it functions as the noun of the sentence because it is the condition or situation being described.