复合树脂充填洞形制备的特点是（）。
A.底平壁直，洞形必须达到一定的深度
B.点线角应圆滑，洞缘角应制备短斜面
C.应制备典型的箱状洞，并设计良好的固位形
D.洞缘角应呈直角，不宜在洞缘角制备短斜面，需去净无基釉
E.无须去净无基釉，但要有良好的抗力形
参考答案：B
解析：基于复合树脂的性能和粘接机制，其窝洞制备相对保守，对固位形要求较银汞合金低。
The hippo(河马) is the most dangerous animal in Africa, but that hasn’t stopped a South African animal lover from making friends with one. Marius Els is 40 years old. He ______ around 20 different kinds of animals on his ranch(饲养场),in South Africa. He has a real soft spot for Humphrey, a 6-year-old hippo that’s like a son to him. While all of his friends are too ____ to go near the animal, and his wife told him not to get too close, Marius climbs on Humphrey’s back as he swims ______ the lake. Marius has kept the hippo_______ he was just five months old. And over the years, the two have________ a special relationship that people just don’t understand. Marius looks on Humphrey as a son, although the 1,200 ton animal could ________ a person with ease. Only sometimes the hippo can throw Marius off his _______ in the water. Humphrey is very friendly to his owner, especially after Marius offers him a dinner of his favorite ________, apples. Humphrey feels very in his life. He had another good friend, a goat, but she got eaten by a jackal(豺), so now he’s all by . Marius says he’s been trying to get a female friend for Humphrey, but there’s no such thing in Africa right now.
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