对流传热的条件是（）和（）。

某一滑动面为折线型的均质滑坡，某主轴断面和作用力参数如下图和下表所示，取滑坡推力计算安全系数γ1=1.05，则第③块滑体剩余下滑力F3最接近（）。

A.1.36×104kN/m

B.1.80×104kN/m

C.1.91×104kN/m

D.2.79×104kN/m

环境卫生学的研究对象包括（）。

A.生活居住环境

B.自然环境和生活环境

C.大气圈，土壤岩石圈和生物圈

D.以上都是

E.以上都不是

Security was such a major concern at the G8 Summit that no journalists could approach the meeting zone without ________ the special pass.[      ]

A. producing

B. issuing

C. commanding

D. involving

   Family quarrels and lack of free time can promote headaches in children. This is what Jennifer Gassmann and her partners have concluded in a study that appears in the current issue of the Deutsches Arzteblatt International. This study was a component of a large-scale study entitled “Children, Adolescents, and Headaches”, in which data were collected in four annual “waves” from 2003 to 2006.

Up to 30% of children around the world complain of headaches at least once a week. Out of a variety of possible factors tested in a larger study, the authors chose to look at the ones related to the children’s family and leisure time.

According to the study, boys who experience more than one family quarrel per week have a 1.8 times higher risk of developing headaches. The amount of free time available to them seems to be even more important: boys who seldom have time to themselves have a 2.1 times higher risk of developing headaches.

The behavior of parents when children complain of headaches also seems to play a major role. Both positive and negative responses from parents teach children that they can gain advantages from headaches. These responses have a particularly strong effect on the frequency of symptoms in girls, with supportive responses raising the risk of recurrent(周期性的) headaches by 25%.

The genders also differed with respect to headache frequency. Twice as many girls as boys had their symptoms at least once a week. The ages of the children, however, seemed to have no more than a minor effect on their headaches.

The study may become a reminder for parents, especially for those unpeaceful families.

68. What is the passage mainly about?

A. How family quarrels and lack of free time can promote headaches in children.

B. A new study on the frequency of headaches in children.

C. Factors which lead to children’s having headaches.

D. Advice for parents wanting to keep their children from having headaches.

69. We learn from the study that ______________.

A. most children have headaches at least once a week

B. the way a family behaves is the chief factor for the headaches of children

C. parents are to blame for the increase in headaches in children

D. girls are more likely to get headache symptoms than boys

70. Parents should learn from the passage that ______________.

A. they should spend more time with their children

B. they should avoid quarreling

C. they shouldn’t care when their children have headaches

D. they should treat boys and girls differently

关于布氏杆菌病的流行病学特点，错误的是（）

A.病后可获较强的免疫力，各型之间无交叉免疫

B.国内以羊为主，其次为牛、猪

C.传播途径以皮肤为主

D.人群普遍易感，牧区感染率最高

E.传染源主要为病畜