機器
architecture
background
barrier
blue
bolt
building
chain
channel
close
concrete
construction
control
dam
electricity
engineering
environment
equipment
flood
floodgate
gate
gear
industrial
industry
iron
lake
lock
machinery
mechanism
metal
nature
old
open
plant
power
river
rusty
screw
sky
sluice
steel
system
technology
thread
toilet
valve
vintage
wheel
white