21.   The sludge later clog river systems and swamp entire villages, and harden like concrete after the waters ebb.

v. + system >>共 729
use 5.91%
develop 3.39%
have 2.88%
change 2.32%
install 2.22%
set_up 2.03%
build 1.69%
create 1.66%
test 1.51%
design 1.34%
clog 0.20%
clog + n. >>共 197
street 15.03%
road 9.97%
artery 7.10%
system 2.87%
traffic 2.73%
court 2.46%
drain 2.46%
middle 2.32%
highway 2.32%
line 1.91%
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