The correct option is C Noun Clause
A clause is a part of a larger sentence containing a subject and a predicate of its own.
A Principal Clause is an independent clause which can exist even without a subordinate clause. A Subordinate Clause is called a dependent clause because it cannot exist without the help of the principal clause. It begins with a subordinating conjunction.
In this sentence, 'I fear' is the principal clause and 'that I shall fail' is the subordinate clause.
The subordinate clause acts as the object of the verb 'fear' in the principal clause thereby acting as a noun. Hence, it becomes a subordinate noun clause.
So, Option A becomes correct and the other three cancel out.