什么是好的发泡剂？
参考答案：
好的发泡剂应该兼有动物性及植物性发泡剂的优点，具有强度高，坚硬性好，流动性好，独立气孔，发泡后气泡有一定的稠度，触摸后有弹性，消泡慢，发泡倍数高等特点。不合格的发泡剂使发泡水泥出现塌陷和沉淀现象。好的发泡剂，在泵送时破碎率由30%降低到15%左右，提高了强度的发泡剂由于稠度高，在泵送过程中形成的气泡群更坚固，不易破碎。
| The first and most important agents of socialization are the people who care for infants. In the earliest months, messages from nurturers constitute the child’s basic understanding of the world around it. This is the infant’s first introduction to the language that shapes perception and elicits emotion. Another powerful source of information and socialization is the friendship of peers. Peers are equals that one can deal with on the same level as oneself, whereas parents are superiors. The heavy emotional overlay of family relationships makes some kinds of learning difficult. Much formal socialization is placed in the hands of professionals. Teachers from kindergarten on are specifically designated agents of socialization. Ideally, a teacher is one who has both knowledge and the skills to present it. During the course of teaching their subjects, classroom instructors provide role models and attempt to convey the excitement of learning itself. In earlier times, parents, friends and teachers would comprise the list of primary childhood socializers. Children’s books, comics and magazines might also have been mentioned as sources of information on norms and role models. Today one must add three powerful indirect or nonpersonal socialization agents: radio, movies and television. Many people learn about politics, form a vision of well-being, and develop attitudes towards others from what they see on the screen and hear through the speakers. |
In this passage, agents of socialization refer to ______.
A．the media
B．individuals
C．all channels
D．organizations