STRUCTURES
ARTIFICIAL
RESISTANT
NATURAL
STABLE
O
I
S
F
S
E
H
E
A
U
R
E
O
D
A
X
T
O
L
W
P
R
M
R
S
Y
R
P
A
P
A
M
Y
A
L
M
E
F
T
L
B
E
R
O
Q
A
U
Z
R
F
I
O
L
Z
U
E
N
W
V
H
U
E
F
C
E
O
T
S
S
U
F
C
T
A
I
O
Y
O
A
J
O
B
O
Y
C
D
C
C
X
K
N
U
Q
A
M
A
U
F
I
T
U
P
S
R
E
Q
J
O
R
O
A
W
J
D
O
U
A
A
X
M
T
P
L
B
W
H
D
G
O
W
I
T
S
V
R
E
S
I
S
T
A
N
T
R
