选B is listening 因为前面一句：Don't interrupt him.可知这事是正在发生,所以用正在进行时
Don't interrupt him.He is listening to the weather forecast.
翻译：
不要打断他.他正在听天气预报.Subway Line5 ___.A.is now constructing B.is constructed now C.is now being constructed D.has now been constructing