简述一下我国对外开放的发展格局如何？ _____________________

下列哪种疾病是非器官特异性自身免疫疾病（）

A.重症肌无力

B.慢性甲状腺炎

C.慢性溃疡性结肠炎

D.系统性红斑狼疮

E.特发性血小板减少性紫癜

急性毒性试验的观察周期一般为（）

A.19天

B.24天

C.14天

D.30天

E.90天

In the following essay, each blank has four choices. Choose the best answer and write down on the answer sheet.
Microwave communication uses high-frequency (26) waves that travel in straightlines through the air. Because the waves cannot (27) with the curvature of the earth, they can be (28) only over short distance. Thus, microwave is a good (29) for sendingdata between buildings in a city or on a large college campus. For longer distances, the waves must be relayed by means of "dishes" or (30) . These can be installed on towers, high buildings, and mountain tops.

A．optical

B．radio

C．electrical

D．magnetic

快门线常常在（）时候用

A.较慢快门

B.较快快门

C.中速快门

D.无所谓

蔬菜种子的播前处理包括哪些内容？