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.

Each paragraph is a self contained unit: the first sentence is the 'topic sentence'; the last sentence is the 'link sentence' and the remaining sentences develop the subject within each paragraph.

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.