正常情况下，焊接电弧的轴线总是沿着电极中心线的方向，电弧的这种性质叫( )。A．电

基于如下描述：设有一个数据库，包括S、J、P、SJP四个关系模式如下：供应商关系模式S(SNO，SNAME，CITY) 零件关系模式P(PNO，PNAME，COLOR，WEIGHT) 工程项目关系模式J(JNO，JNAME，CITY) 供应情况关系模式SJP(SNO，PNO，JNO，QTY) 假定它们都已经有若干数据。“找出使用供应商名为‘红星’的供应商所供应的零件的工程名”的SELECT语句中将使用的关系有( )

A．S、J和SJP

B．S、P和SJP

C．P、J和SJP

D．S、J、P和SJP

市盈率模型最适合连续盈利，并且β值接近于1的企业。（）

眼底检查对于C／D大于（）或双眼C／D之差大于的患者，考虑是否有开角型青光眼的可能性。

For many people today, reading is no longer relaxation. To keep up their work they must read letters, reports, trade publications, interoffice communications, not to mention newspapers and magazines: a never-ending flood of words.
In (36) a job or advancing in one, the ability to read and comprehend (37) can mean the difference between success and failure. Yet the unfortunate fact is that most of us are (38) readers.
Most of us develop poor reading (39) at an early age, and never get over them. The main deficiency (40) in the actual stuff of language itself—words. Taken individually, words have (41) meaning until they are strung together into phrases, sentences and para-graphs. (42) , however, the untrained reader does not read groups of words. He laboriously reads one word at a time, often regressing to (43) words or passages.
Regression, the tendency to look back over (44) you have just read, is a common bad habit in reading. Another habit which (45) down the speed of reading is vocalization—sounding each word either orally or mentally as (46) reads. To overcome these bad habits, some reading clinics use a device called an (47) , which moves a bar (or curtain) down the page at a predetermined speed. The bar is set at a slightly faster rate (48) the reader finds comfortable, in order to "stretch" him.
The accelerator forces the reader to read fast, (49) word-by-word reading, regression and sub vocalization, practically impossible. At first (50) is sacrificed for speed. But when you learn to read ideas and concepts, you will not only read faster, (51) your comprehension will improve.
Many people have found (52) reading skill drastically improved after some training. (53) Charlce Au, a business manager, for instance, his reading rate was a reasonably good 172 words a minute (54) the training, now it is an excellent 1,378 words a minute. He is delighted that how he can (55) a lot more reading material in a short period of time.

[A] training [B] habits [C] situations [D] custom

埋弧焊属于熔化焊（）.