问题 选择题

不能用来判断蜡烛发生化学变化的现象是

A.用白瓷菜碟盖在蜡烛火焰上,在白瓷板上可观察到黑色的粉末状物质

B.蜡烛燃烧时发光、发热

C.在火焰上罩一个干而冷的烧杯,烧杯内壁出现水雾

D.用内壁蘸有澄清石灰水的烧杯罩在火焰上方,烧杯内壁出现白色浑浊物

答案

答案:B

A、用白瓷菜碟盖在蜡烛火焰上,在白瓷板上可观察到黑色粉末状物质,说明蜡烛不完全燃烧生成了碳,属于化学变化,故A错误;

B、发光、放热是化学变化中常常伴随的现象,但是发光放热并不能说明一定发生了化学变化,例如,电灯通电时也发光放热,但是不属于化学变化,故B正确;

C、在火焰上罩一个干而冷的烧杯,烧杯内壁出现水雾,说明有新物质水生成,属于化学变化,故C错误;

D、用内壁蘸有澄清石灰水的烧杯罩在火焰上方,烧杯内壁出现白色浑浊,说明生成了新物质二氧化碳,属于化学变化,故D错误;

故选B.

单项选择题
单项选择题

(B)

My father was chief engineer of a merchant ship, which was sunk in Word War Ⅱ, The book Night of the U-boats told the story.

Memories

In September, 1940, my mother, sister and I went to Swansea, where my father’s ship was getting ready to sail. We brought him a family photograph to be kept with him at all times and keep him sale.

Then I remember my mother lying face down, sobbing. She had heard from a friend that the ship had been sunk by a torpedo(鱼雷).

I can remember the arrival of the telegram (电报), which in those days always brought had news. My grandmother opened it. It read, "Safe. Love Ted."

My most vivid memory is being woken and brought down to sit on my father’s knee, his arm in a bandage.

He was judged unfit to return to ea and took a shore job in Glasgow for the rest of the war. For as long as I can remember, he had a weak heart. Mother said it was caused by the torpedoes. He said it was because of the cigarettes, whichever, he died suddenly in his early 50s.

Ten years later I read Night of the U-bouts and was able to complete the story.

Torpedo

One torpedo struck the ship; Father was in the engine room, where the third engineer was killed. He shut down the engines to slow the ship making it easier for it to be abandoned.

By the time he got on desk (甲板) he was alone. Every lifeboat was gone except one which had stuck fast. When he tried to cut it free, it swung against the ship, injuring his hand and arm. He had no choice but to jump—still with the photograph in his pocket.

Three days later, he and other survivors were safe in Glasgow. All 23 with him signed the back of the photograph.

A Toast

In my room is the book and the photograph. Often, glass in hand; I have wondered how I would have dealt with an explosion, a sinking ship, a jump into a vast ocean and a wait for rescue Lest(以免)we forget, I have some more whisky and toast the heroes of the war.

What can we know about the author’s father after his ship was attacked()

A. He lost his arm.

B. He repaired the engines.

C. He managed to take a lifeboat.

D. He was the last to leave the ship.