their hard exoskeletons had served as useful armor underwater. 坚硬的外骨骼在水下是有用的护甲
with those backpacks. Find something useful. 找点有用的
A useful talent, I'm sure you'd agree. 很实用的才能,我相信你也同意
will certainly be useful later in life in these flooded mangrove forests. 将来会成为在红树林中 非常有用的生活技能