Read the text and choose the best answer (A, B, C, or D).         

    Being over-shadowed by Ha Long Bay to the North, Cat Ba Island is often left out of the itineraries of the majority of travelers coming to Viet Nam. Nevertheless, Cat Ba Island is one of the most underrated destinations in Viet Nam. The park possesses seven different ecosystems, both underwater and inland. It is home to thirty-two types of mammals, along with seventy bird species, and more than a thousand species of plants, hundreds of which can be used as medicines.             There are several different hiking and trekking routes through rugged and forested mountain within Cat Ba National Park. These routes are also divided by different levels of difficulty, so travelers don’t have to be worried if their fitness is not very good. In addition, travellers can take a side visit to explore the exquisite Trung Trang cave, or discover the traditional village of Viet Hai. 

1. Many travellers choose not to visit Cat Ba Island because ……………………..