they can never let down their guard... 也绝不能放松戒备

29. they've found themselves in a world of plenty.
    它们进入了一个丰饶的世界
30. Some, like Diplodocus, have grown to become 25 meters long.
    有一些恐龙 比如梁龙 长到25米长
31. But even at their size,
    即便体型如此庞大
32. they can never let down their guard...
    也绝不能放松戒备
33. ...for they aren't the only giants of the Jurassic.
    因为它们不是侏罗纪时代唯一的巨兽
34. Allosaurus.
    异特龙
35. Nearly nine meters long...
    将近九米长

来自《我们星球上的生命 第一季 第五集 Life on Our Planet S01E05 巨兽阴影下》第 32 行