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Bubby has got a doorbell. If you visit him, you must ring his doorbell.
One day, Mr. Panda visited him. He knocked at his door. He knocked and knocked. After a while, Bubby shouted in the room, "Please ring the doorbell!" But Mr. Panda didn't hear it. He knocked again. This time, Bubby opened the door and said, "Don't knock at the door. I can't hear. Ring the doorbell, please."
1．Bubby doesn't have a doorbell. （2．One day, Mr. Panda visited him and rang the doorbell. （
3．Bubby didn't at home that day. （
4．Bubby asked Mr. Panda to ring the doorbell. （
同类型试题
y = sin x， x∈R， y∈[–1，1]，周期为2π，函数图像以 x = (π/2) + kπ 为对称轴
y = arcsin x， x∈[–1，1]， y∈[–π/2，π/2]
sin x = 0 ←→ arcsin x = 0
sin x = 1/2 ←→ arcsin x = π/6
sin x = √2/2 ←→ arcsin x = π/4
sin x = 1 ←→ arcsin x = π/2
y = sin x， x∈R， y∈[–1，1]，周期为2π，函数图像以 x = (π/2) + kπ 为对称轴
y = arcsin x， x∈[–1，1]， y∈[–π/2，π/2]
sin x = 0 ←→ arcsin x = 0
sin x = 1/2 ←→ arcsin x = π/6
sin x = √2/2 ←→ arcsin x = π/4
sin x = 1 ←→ arcsin x = π/2
