The more points of contact your back can have with a contoured and supportive seatback, the better.

你的背部与轮廓和支撑椅背的接触点越多越好。

Look at how flat the seatback of this plane chair is.

看看这把飞机座椅的靠背有多平。

Now, in preparation for take-off, please fasten your seatbelt, return your seatback and tray tables to the full upright and locked position.

现在，为起飞做准备， 请系好安全带，将座椅靠背和小桌板恢复到完全直立并锁定的位置。

If passengers could adjust the depth of their seat pan, it would help them support their knees and be able to sit fully against the seatback.

如果乘客可以调整座椅的深度，这将有助于他们支撑膝盖，并能够完全靠在椅背上。

Yeah, maybe. Meanwhile back in the 21st century, people are raising their tray tables and putting their seatbacks in an upright position 'cause it's time to land in San Francisco.

可能。这个时候21世纪的人在准备收起折叠桌，将座椅调整到竖直状态，因为飞机要着陆到旧金山了。

It also tells you to " return your seatback and tray tables into the full upright and locked position." Couple of different phrases or words here, first of all, " seatback."

它还告诉您“将座椅靠背和托盘桌恢复到完全直立和锁定的位置。 ” 这里有几个不同的短语或词， 首先是“座椅靠背” 。