问题 填空题

三相对称,同名相的电流和电压同时加入功率方向继电器,继电器中的电流和电压正好相差()、这种接线称90°()。

答案

参考答案:90°;接线

单项选择题
单项选择题

A controversial decision on whether choice cuts of steak and cartons of milk produced from cloned animals are suitable for the dinner table is now long overdue.

Hundreds of pigs, cows and other animals created with the help of cloning are living (1) farms across the United States and (2) the forthcoming ruling will directly (3) American consumers, British holidaymakers may also (4) themselves at the forefront of a food revolution that many commentators expect will (5) arrive here.

(6) the birth of Dolly the sheep-the first mammal cloned from an adult cell--there were extreme predictions of herds of genetically (7) bulls and pastures (8) with cloned dairy cows.

That double (9) of the past decade has not yet been realized (10) clones have become a familiar sight at agricultural fairs in America, where producers of (11) pigs and cattle have been among the first to (12) cloning, which offers a way to keep (13) traits without inbreeding problems caused by traditional methods. Clones of rare and elite animals, including sheep, goats, and rabbits, (14) a way to improve animal healthy, (15) the nutritional value of meat and milk, and breed animals immune (16) diseases or better suited for developing countries.

The safety of cloned (17) has been under examination by various bodies. Three years ago the US National Academy of Science concluded that (18) available data indicated that cloning met animal welfare and food safety considerations, more information was needed. (19) scientific evidence suggests that there is little (20) for alarm, at least on food-safety grounds.

19()

A.propose

B.offer

C.exhibit

D.present