passage twoQuestions 30 to 32 are based on the passage you have just heard.
A. Kings and queens, princes and princesses, and lords and ladies built castles in order to get more land. .
B. Around the outside of a castle, a moat was dug, which was often filled with water.
C. A castle was built behind a thick end high stonewall, which was strong enough to stand the possible attack of enemies.
D. If a drawbridge was pulled up, there was no way for people to enter the castle.
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物质循环又称为生物地球化学循环,是指各种化学物质在生物和______之间的循环运转。
鱼类种群内较小的个体比大的个体更有利于躲避捕食者,那么小的个体就会有更高的存活率并能留下更多的后代,这说明鱼类个体在______上是存在差异的。
80x86CPU寄存器中负责与I/O端口交换数据的寄存器为 【8】 。
植物之间为竞争环境条件和动物之间为了争夺食物,都会导致______分布的不均匀,形成镶嵌性。