题目内容：
请在第__(50)__处填上正确答案。
A．But this advantage also has a big drawback up to % of the biggest toads suffer from arthritis. B．The task now facing the country is how to remove the toads.
C．But arthritis didn't slow down toads outside the laboratory.
D．Toads with longer legs move faster and travel longer distances while the others are being left behind.
E．Toads are not built to be road runners -- they are built to sit around ponds and wetareas.
F．Furthermore, they soon take over the natural habitats of Australia's native species.
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