primary bone

例句：

1. 1. The primary goal of the project is to improve efficiency.
   该项目的首要目标是提高效率。
2. 2. He was the primary caretaker of his family during his absence.
   在他缺席期间，他是家庭的主要照顾者。
3. 3. This is the primary reason for their success.
   这是他们成功的主要原因。