2. Although biologists can easily induce extra limbs to grow on the flank of a

tetrapod">tetrapod

, this cannot be done in the neck.

虽然生物学家能轻易让四足动物在侧腹长出额外的肢，在颈部却做不到。

3. But the nickel disappearance is one more clue about how the planet went from suffocating to a place where a terrestrial

tetrapod">tetrapod

could take a deep breath.

但是对于如何解释我们的地球从一个令人窒息的环境转变为一个让陆地四足动物可以自由呼吸的地方，镍的消失又提供了一个线索。

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back-to-front

参考例句

1. The front-and-back registration of gripper bars adds adjustable device, convenient to adjust the precision of front lay.

牙排的前后定位增加可调装置，以便调整前规精度；

2. A man-tapered shirt with yoke at front and back, a pointed collar, two patch pockets with flaps and fancy snap closures on front placket and cuffs.

前后幅都有育克的男装修长衬衫，尖领，两个有袋盖的明贴袋，且前中开口与袖口都以新潮按扣扣合。

3. A man-tapered shirt with yoke at front and back, a pointed collar, two patch pockets with flaps and fancy snap closures on front placket and cuffs.

前后幅都有育克的男装修长衬衫，尖领，两个有袋盖的明贴袋，且前中开口与袖口都以新潮按扣扣合。 4. Unusually deep front to back for a small lathe the saddle carried an almost boring-table sized T-slotted cross slide fitted with a "bridge bracket" at the front.