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