第一步：NaNO₂+NH₄Cl=NaCl+NH₄NO₂

第二步：NH₄NO₂=N₂↑+2H₂O

下列对第二步反应的叙述中正确的是(    )

①NH₄NO₂只是氧化剂 ②NH₄NO₂只是还原剂

③NH₄NO₂发生了分解反应 ④只有氮元素的化合价发生了变化

⑤NH₄NO₂既是氧化剂又是还原剂

戈尔巴乔夫改革背景不包括（ ）

    Li Ping is going to England. He wants to know something about English people. One day he sees an English girl in the street. Then he comes up to her.

    “Excuse me, may I ask you some questions?”

    “Of course you may.” answers the girl politely.

    “I'll go to London. What should I notice when I'm talking with English people in London? ”asks Li Ping.

    “Well, don't ask a woman how old she is and…”

    “But how old are you? ”Li Ping stops the girl and asks suddenly.

    “I…”The girl gets angry.

    “Why do you get so angry?”asks Li Ping. “Now we are in China, not in England, you see”

下列四幅地貌景观图中，因侵蚀作用而形成的地貌是