以下为句子列表：
英文: Unfortunately, the solid propellants—usually aluminum fuel and ammonium perchlorate oxidizer—burn fairly inefficiently, are toxic to the environment, and are difficult to fabricate and handle safely.
中文: 然而固体推进剂（通常是铝燃料和过氯酸铵氧化剂）燃烧效率颇低、对环境有害，而且很难安全地制造和操作。
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