题目

The old palace looks so great! I heard that it _______ nearly 1000 years ago.     A. was building    B. was built       C. has built         D. is built 答案：B结黄色种子（Aa）和结绿色种子（aa）的豌豆杂交，它们后代的性状表现和比例是（ ）A．黄色种子∶绿色种子＝1∶1 B．黄色种子∶绿色种子＝2∶1C．黄色种子∶绿色种子＝3∶1 D．黄色种子∶绿色种子＝4∶1