我国四大工业基地中，以重工业为主的是

自尊是成才和成功者必备的心理品质，是成才与成功的重要条件。（    ）

近年来，黄河水文情势发生了很大变化，中游地区尤为明显。头道拐和龙门是黄河中游地区两座水文站，窟野河是其间一条支流。读不同时期头道拐和龙门水文站水沙变化表，完成以下问题。

    Tom was only seven years old. He likes watching ____ very much. He ____ went to the movies before. One day, he ____ to have a try. When getting to the cinema, he bought a ticket (票) and went in. ____ after two or three minutes, he came out, and bought the second ticket and went in. After a few minutes, he came out again and bought the third ticket. 

    Then a girl ____ about him and asked, “Why do you buy so many tickets? How many friends do you meet?” “No, I have no friends here, but a woman always stops me at the door and tears (撕) my ticket.”

某小岛上原有果蝇20000只，其中基因型VV、Vv和vv的果蝇分别占15%、55%和30%．若此时从岛外入侵了2 000只基因型为VV的果蝇，且所有果蝇均随机交配，则F₁代中V的基因频率约是（　　）