若有氢气和氧气各一瓶（如图所示），其中B瓶盛放的气体是____ ．

下列动物的行为中，属于学习行为的（ ）

李四光的地质力学理论在我国的石油勘探、铀矿资源寻找等方面发挥了重大的指导作用。该理论作为新学科正式载入史册是

②化简： $\frac{2x}{x^2-4}-\frac{1}{x-2}$ ．

    Are you ready for adventure (冒险)? Then Sunny Shores Sea Camp is the place for you! The activities there are all about the sea.
At Sunny Shores Sea Camp, you can get excited and improve your skill-level. You can enjoy the wonders of Sunny Island. From diving（潜水）to sailing, sea science to seafood, Sunny Shores Sea Camp offers courses for your different interest. You can also learn about the sea environments of Sunny Island. It is hard for you to find anywhere else like that.
    Whether you're a beginner or already an expert (专家), Sunny Shores Sea Camp is a great place that brings together campers from all over the world.
    Wonderful memories and new friends are waiting for you at Sunny Shores Sea Camp!
Camp Activities: Adventure . Sea Biology. Diving . Sailing . Windsurfing
Camp Address: Sun Bay , South Florida 000634
Dates: June 28 - July 18 , July 21 -August 9
Cost Week: $600 - $900
Campers Ages: From 13 to 17
Contact us: Sign up at www.sunnyshoresseacamp.org! Or call 800-645-14231