In the questions given below, a part of the sentence is underlined. Below each sentence, some phrases are given which can substitute the underlined part of the sentence. Identify the phrase which can correctly substitute the underlined part of the sentence. If the sentence is correct, as it is, the answer should be 'no improvement is required'.

Due to the scarcity of hurricanes near the coast, a beach house must have sturdy walls to prevent it from collapsing.