填空题 Y (for YES) if the statement agrees with the information given in the passage;
N (for NO) if the statement contradicts the information given in the passage;
NG (for NOT GIVEN) if the information is not given in the passage.
For questions 56---59, complete the sentences with the information given in the passage.

填空题 Frogs are disappearing only from city areas.

填空题 Biologists are unable to explain why frogs are dying out.

填空题 Attempts are being made to halt the development of wet marshland.

填空题 Frogs are important in the ecosystem because they control pests.

填空题 It is not known why Dutch frogs are changing colour.

填空题 It is a fact that frogs' breeding cycle has been upset by worldwide increases in temperature.

填空题 The decline in the numbers of frogs worldwide may be warning us of a ______.

填空题 One danger to the Earth because of decreasing frog numbers is that we may ______ in the ecological food chain.

填空题 Some unknown contributory factor is turning frogs yellow and / or orange in the ______.

填空题 ______ has led to a sharp increase in ultraviolet radiation levels.