A：亚洲
B：欧洲
C：北美洲
D：南美洲
所谓“要式买卖”……是罗马法移转所有权最古老的方式。采用“要式买卖”时，当事人（主要是罗马市民）必须亲自到场，并由已达婚龄的市民五人出场作证，另由一已达婚龄的市民为司秤人。买卖时，由司秤人持秤，买受人一手持标的物或其象征物，一手持铜块说：“依照罗马法律，此物应归我所有，我是以此铜块和秤买来的”。说毕，以铜块击秤，随即交给出卖人，买卖就告成立，买受人立即取得所有权。材料表明，罗马法的特征是（ ）
Gypsies
According to the linguistic and genetic researches, ancestors of the Gypsies left the land of India in the amount that did not go beyond 1,000 people. Today there are about 10 million Gypsies in the world. Some scientists believe that Gypsies were Egyptians.
Sumerians
Sumerians must be the mysterious people in the ancient world. We know nothing about their origin and nothing about the origin of their language. The Sumerians were rather advanced—they became the first in the Near East to use a wheel, to create an irrigation system and their unique writing. And besides, they were impressively good at maths and astronomy.
Maya
Some scientists believe that they are connected to legendary atlantes (男像柱), others suppose their ancestors were Egyptians. It's thought that the Maya created an efficient agricultural system and had deep astronomy knowledge. Their calendar was used by other people of Central America. Maya applied the hieroglyphic writing (象形文字) system. Now it seems that the Maya came from nowhere and disappeared nowhere.
则：
平均命中环数为____；命中环数的方差为____．
选出与题干中加线词含义相同的一项（）
如履平地___________
