平行四边形的内角和是______，它有______组对边分别平行．
平行四边形的内角和是360°，它有两组对边分别平行；
故答案为：360°，两．
Most environmental problems exist because ______ measures for preventing them have not been
taken in the past.[ ]
A. accurate
B. extreme
C. tentative
D. adequate
东非大裂谷是遗痕期大洋。
