The abdominal aorta is normally smaller than the thoracic aorta.是什么意思？

The abdominal aorta is normally smaller than the thoracic aorta.

腹主动脉一般比胸主动脉小.

the

art. 指已提到的人（物），指说话人与听者已知的人（物），用于独一无二的事物前，与形容词最高级和序数词连用；

例句
He did have a real knowledge of the country...
他对该国的确知之甚多。

abdominal

adj. 腹部的，[鱼]有腹鳍的；n. 腹肌（常用作复数）；

例句
...vomiting, diarrhoea and abdominal pain.
呕吐、腹泻和腹痛

aorta

n. 主动脉；

例句
The abdominal aorta is normally smaller than the thoracic aorta.
腹主动脉一般比胸主动脉小.

is

vt.& vi. 是（be的三单形式；n. 存在；

例句
Bollinger 'RD' is a rare, highly prized wine.
博林格RD香槟是一种名贵的备受推崇的葡萄酒。

normally

adv. 正常地，通常地，一般地，按说，论理；

例句
They don't normally give any advance notice about which building they're going to inspect...
他们一般不会预先通知检查哪座大楼。

smaller

adj. 更小的，小的( small的比较级 )，小气的，（服装、食品、家用设施等）小号的，小规模的；

例句
More than 750 commercial airliners were involved in fatal accidents last year. Added to that were the 1,550 smaller aircraft.
去年750多家商业航空公司遭遇过人员死亡的事故。另外还有1,550架小型飞机也出过同样的事故。

than

conj. 比（用于比较级），宁愿…而不愿，除…以外，一…就；prep. 超过，比；

例句
...more than a thousand acres of land.
1,000多英亩地

thoracic

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例句
The abdominal aorta is normally smaller than the thoracic aorta.
腹主动脉一般比胸主动脉小.