According to the passage, a life preserver should be first of all ______.

参考解析：

推理判断题。根据第三段“The position in which the life preserver will support a person who jumps or falls into the water is the most important, as is its tendency to turn the wearer in the water from a face-down position to an upright or slightly backward position, with his face clear of the water, even when the wearer is exhausted or unconscious.”可知，救生衣支撑跳入或掉进水中的人的位置是最重要的，因为它会使水中的穿戴者从面朝下的姿势转为直立或略向后的姿势。由此可推知救生衣首先能够自动扶正以调整落水者的位置。self-righting意为“自动扶正”；self-positioning意为“自我定位”；comfortable意为“舒适的”；durable意为“耐用的，持久的”。故选A。