如图所示，有两根长均为L、质量均为m的细导体棒a、b，其中a被水平放置在倾角为45°的绝缘光滑斜面上，b被水平固定在斜面的右侧，且与a在同一水平面上，a、b相互平行。当两细棒中均通以大小为I的同向电流时，a恰能在斜面上保持静止，关于b的电流在a处产生的磁场的磁感应强度B，下列说法正确的是

A．方向竖直向上

B．大小为

C．大小为

D．若使b竖直向下移动，a仍能保持静止

People are indulging in an illusion whenever they find themselves explaining at a cocktail(鸡尾酒 ) party, say, that they are "in computers," or " in telecommunications," or "in electronic funds transfer". The implication is that they are part of the high-tech world. Just between us, they usually aren’t. The researchers who made fundamental breakthroughs in those areas are in a high-tech business. The rest of us are (11) of their work. We use computers and other new technology components to develop our products or to organize our affairs. Because we go about this work in teams and projects and other tightly knit working group(紧密联系在一起的工作小组 ), we are mostly in the human communication business. Our successes stem from good human interactions by all participants in the effort, and our failures stem from poor human interactions.
The main reason we tend to focus on the (12) rather than the human side of work is not because it’s more (13) , but because it’s easier to do. Getting the new disk drive installed is positively trivial compared to figurine out why Horace is in a blue funk(恐惧)or why Susan is dissatisfied with the company aver only a few months. Human interactions are complicated and never very crisp(干脆的,干净利落的) and clean in their effects, but they matter more than any other aspect of the work.
If you find yourself concentrating on the (14) rather than the (15) , you’re like the vaudeville character(杂耍人物)who loses his Keys on a dark street and looks for them on the adjacent street because, as he explains, "The light is better there!\

A．technology

B．sociology

C．physiology

D．astronomy