侵蚀性葡萄胎可来源于（）. A.早期流产 B.异位妊娠 C.晚期流产 D.足月妊娠

已知地球半径为R、地球同步卫星的轨道半径为r．假设地球赤道上的物体随地球自转的向心加速度为a₁，第一宇宙速度为V₁，地球近地卫星的周期为T₁；假设地球同步卫星的运行速率为V₂，加速度为a₂，周期为T₂．则下列比值正确的是（　　）

A．

B．

C．

D．

阅读理解。

     Almost all theme park accidents can be prevented. Here, based on theme park safety, are some tips to help

you and your family stay safe on your next visit.

     Stay Cool, and Don't Get Burned

     Heat causes more pain and injury at theme parks than all the world's roller coasters (过山车) combined.

Water is your best friend in helping p.revent heat-related illnesses in theme parks. Choose water rather than

juice and soft drinks whenever you get thirsty. Put on a waterproof sunscreen before you enter the park. A

hat or sunglass- es can help, too.

     Stay In to Stay Safe

     On any theme park ride, keep your rear (后部) on the seat, your hands on the grab bar (扶手) and your

feet and knees inside the car. If there is no grab bar, keep your hands on your lap (膝部). If you are riding a

"floorless" coaster, relax your legs. Don't kick them out to the side or front. Do not get on or off a ride until

you've been given the okay by an attendant to do so.

     Help the Kids

     If you are visiting with a child, tell them how they should be have. Meanwhile, parents also know the

following rules, too.

     ★Tell them to stay seated, to hold the grab bar or put their hands in the laps.

     ★And never put a crying child on a ride. If your child starts to cry, let others pass you in line until your

child is calmed. Or, gently exit the queue and find something more relaxing to do.

     ★Let them take plenty of breaks.

     "Kids get tired," said TPI reader Matt Johnson, a father of four. "Tired kids make parents even more tired.

And tired kids and parents get hurt-physically and emotionally." He advises that parefits plan a mid-day break,

perhaps a swim back at the hotel, to avoid mid-day heat and crowds.

     "You will see many families having a miserable time while you are refreshed and having a great evening."

1. The best title for the passage would probably be _____.

A. Theme Park Safety Tips

B. How to Protect Yourselves Better

C. Full Preparations Before Visiting Theme Park

D. Theme Park Accidents

2. The underlined word "miserable" likely means _____.

A. comfortable

B. very unhappy

C. pleasant

D. wonderful

3. We may infer from Matt Johnson's words that _____.

A. he doesn't like to visit a theme park with his children

B. parents with many children may be tired of visiting a theme park

C. not all the families are relaxed or happy when they visit a theme park

D. parents should plan a mid-day break or a swim back at the hotel to avoid heat and crowds.

企业的运行都应当有生产经营条件，一般来说把固定资产和流动资产称之为

A．经济流量

B．经济存量

C．经济产出

D．经济效益

安全色包括（）。

A、红色

B、蓝色

C、黄色

D、绿色

0.35MPa下天然气的液化温度约为（）。

A.-83℃

B.-145℃

C.-162℃

D.-182℃