Directions: In the following sentence, three substitutions are given for each italicised part. If one of them is better than the italicised part, that should be your answer. If none of the substitution improves the sentence, the answer should be (4).

His sudden departure demonstrates that how unreliable he is.

When 'demonstrate' is used to show someone's characteristic or quality, it's followed directly by a noun clause without 'that'. The clause 'how unreliable he is' correctly functions as the noun clause. The 'that' in the original sentence is grammatically redundant and incorrect. Therefore, 'how unreliable he is' is the correct improvement.