生长快,收益早,产量高,质量好,收获期长是()树种选择依据。A.用材林 B.防护林

题型:单项选择题

问题:

生长快,收益早,产量高,质量好,收获期长是()树种选择依据。

A.用材林

B.防护林

C.经济林

D.薪炭林

考点:环境科学技术及资源科学技术森林培育学森林培育学题库
题型:单项选择题

下列说法中正确的是(  )

A.体积、质量都很大的物体一定不能看成质点

B.当研究一列列车全部通过某隧道所需的时间时,因为列车上各点的运动情况相同,所以可以把列车视为质点

C.行走的自行车,因为车轮在转动,所以自行车一定不能视为质点

D.各部分运动状态完全一致的物体可以看作质点

题型:单项选择题

一件工作甲先做6小时,乙接着做12小时可以完成,如果甲先做8小时,乙接着做6小时也可以完成,如乙独做需多少小时完成?

题型:单项选择题

凡与乙炔接触的附件,严禁选用含铜量()的铜合金,以及银、锌、镉及其合金材料。

题型:单项选择题

设计压力就是公称压力。

题型:单项选择题

I was a single parent of four small children, working at a low paid job. Money was always tight, but we had a (1) over our heads, food on the table, clothes on our backs, and if not a lot, always (2) . Not knowing we were poor, my kids just thought I was (3) . I’ve always been glad about that.

It was Christmas time, and although there wasn’t (4) for a lot of gifts, we planned to celebrate with a family party. But the big (5) for the kids was the fun of Christmas (6) .

They planned weeks ahead of time, asking (7) what they wanted for Christmas. Fortunately, I had saved MYM120 for (8) to share by all five of us.

The big (9) arrived. I gave each kid a twenty-dollar bill and (10) them to look for gifts of about four dollars each. Then everyone scattered. We had two hours to shop; then we would (11) back at the "Santa’s Workshop".

Driving home, everyone was in high Christmas spirits, (12) my younger daughter, Ginger, who was unusually (13) . She had only one small, flat bag with a few candies—fiftycent candies! I was so angry, but I didn’t say anything (14) we got home. I called her into my bedroom and closed the door, (15) to be angry again. This is what she told me.

"I was looking (16) thinking of what to buy, and I (17) to read the little cards on the ’Giving Trees’. One was for a little girl, four years old, and all she (18) for Christmas was a doll. So I took the card off the tree and (19) the doll for her. We have so much and she doesn’t have anything. "

I never felt so (20) as I did that day.

5()

A.improvement 

B.problem 

C.surprise 

D.excitement

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