探测面与工件底面不平行时将导致底面回波消失。

阅读下面短文，按照句子结构的语法性和上下文连贯的要求，在空格处填入一个适当的词或使用括号中词语的正确形式填空。

Since the one-baby policy __小题1:____(carry) out in China, Chinese families have been shrinking from one with over 10 members to the other with only three including parents and baaby. Things are usually out of our expectation. Apart from the benefits ___小题2:____ have been mentioned enough, small families are now beginning to have ___小题3:___own problems. Because parents are having fewer children, they increasingly feel the need ___小题4:____(control) the lives of those children. As a result, many children are becoming less ___小题5:____(depend), determined and ambitious than in the past.

Parents today discourage their children from doing housework, extracurricular activities and socializing ___小题6:___ they fear it will interrupt their education. For example, when I was younger I wanted to learn the guitar ___小题7:___ my parents wouldn’t allow me because they believed it would distract me from my studies. They are happy as long as I perform ___小题8:___(wonder) in my exams but don’t seem concerned about how I develop ___小题9:___ a person.

To some extent, I understand parents’ concerns, but I think they should love their children for __小题10:__ they are, not what they want them to be. We deserve the chance to chase our own dreams and learn on our own. Even if we fail, we can learn from those failures.

关于成分输血的优点，叙述最正确的是（）。

A.制品容量小，有效成分的浓度和纯度高，治疗效果好

B.使用相对安全，不良反应少

C.减少输血相关传染病的发生

D.综合利用，节约血液资源

E.以上答案都正确

焊料焊接的基本条件不包括（）

A.润湿性

B.焊件和焊料

C.焊媒

D.还原剂

E.温度

设行向量组（2，1，1，1），（2，1，a，a），（3，2，1，a），（4，3，2，1）线性相关，且a≠1，求a。

带电体之间的放电不一定能点燃可燃蒸气。当放电能量太小时，还没有足够的能量去点燃可燃蒸气。另外即使有足够的放电能量，如可燃蒸气的浓度不在爆炸和燃烧范围内，也不能发生爆炸和燃烧。点燃油品蒸气的最小放电能量约为（）。

A.0.15mJ

B.0.25mJ

C.0.50mJ

D.0.75mJ