尾部又分4段：颈段、中段、主段和末段。
The tail consists of 4 segments: neck region, midpiece, principle piece and endpiece.
主段的中心结构是轴丝。
扩压段应具有一定的长度以保证主气流减速到一定程度。 。
Thee diffuser length should be long enough to ensure the main flow deceleration.
不过主行星在一段时间内几次逆行是平常之事。
It is common for a major planet to retrograde for several months at a time.
不过主行星在一段时间内几次逆行是平常之事。
It is common for a major planet to retrograde for several months at a time.
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