给下列的数据填上恰当的单位． （1）一只钢笔的质量约为21______； （2）

第II卷（共21分）

第四部分 写作（共2节，满分21分）

第一节：单词拼写 (共12小题；每小题0.5分，满分6分)

73. He looks very young, but a___________, he is in his fifties.

74.In that big fire all their houses were completely d___________, so they had to build new ones.

75. Please use the words to make a sentence a___________to the situation.

76. More and more people realize the importance of wildlife p___________.

77. Mike works far away from home and he is always c______about the health of his aging parents.

78. The new model sells well because it is of good q___________ and the price is low.

79. After years of hard work, she s___________ in winning a gold medal in 2008 Beijing Olympics.

80. Can you help me? I have difficulty in s___________ this problem, which upsets me very much.

81. You should take a positive a___________toward life, so you will feel your life full of laughter.

82. We all think highly of the girl who was a___________ into Beijing University last summer.

83. He is a r___________ man, so you can turn to him for help.

84. I believed that nobody could c___________ against him for this position.

反映公司在一定会计期间内，现金和现金等价物流入和流出信息的会计报表，称为( )。

A．资产负债表

B．利润表

C．利润分配表

D．现金流量表

硼、镁及其化合物在工农业生产中应用广泛。

已知：硼镁矿主要成分为Mg₂B₂O₅•H₂O，硼砂的化学式为Na₂B₄O₇•10H₂O。利用硼镁矿制取金属镁及粗硼的工艺流程为：

回答下列有关问题：

（1）硼砂中B的化合价为        ，溶于热水后，常用H₂SO₄调pH2～3制取H₃BO₃，反应的离子方程式为             。X为H₃BO₃晶体加热脱水的产物，其与Mg制取粗硼的化学方程式为               。

（2）MgCl₂·7H₂O需要在HCl氛围中加热，其目的是                           。若用惰性电极电解MgCl₂溶液，其阴极反应式为                 。

（3）镁-H₂O₂酸性燃料电池的反应机理为Mg+H₂O₂+2H⁺==Mg²⁺+2H₂O，则正极反应式为                  。若起始电解质溶液pH=1，则pH=2时溶液中Mg²⁺离子浓度为       。已知Ksp[Mg(OH)₂]=5．610^-12，当溶液pH=6时       (填“有”或“没有”)Mg(OH)₂沉淀析出。

（4）制得的粗硼在一定条件下生成BI₃，BI₃加热分解可以得到纯净的单质硼。现将    0．020g粗硼制成的BI₃完全分解，生成的I₂用0．30mol·L^-1 Na₂S₂O₃(H₂S₂O₃为弱酸)溶液滴定至终点，消耗Na₂S₂O₃溶液18．00mL。盛装Na₂S₂O₃溶液的仪器应为       滴定管(填“酸式”或“碱式”)。该粗硼样品的纯度为       。(提示：I₂+2S₂O₃^2-=2I^-+S₄O₆^2-)

《铁路线路修理规则》规定，焊完后的钢轨焊缝处轨温应降至200℃以下才能放行列车，否则焊缝在列车的载荷作用下，有产生永久变形的可能。

下面哪些是无线网络相对于有线网络的优势（）

A.维护费用低

B.可扩展性好

C.灵活度高

D.安全性更高