Which one of the following sentences would be a good topic sentence (first sentence) for the paragraph below? Although hippos may appear sweet and friendly, they are one of the animals you do not want to tangle with: they are easily frightened and very aggressive. A hippo will not hesitate to attack a human - especially if its young are close by.

The 'topic sentence' introduces us to the subject of the paragraph and the 'link sentence' is a sentence that introduces the next paragraph: this ensures a smooth continuity in the text.