In order to maintain the desired shape of the tunnel, the cross-section of the tunnel must be checked at a regular interval of

In order to maintain the desired shape of the tunnel, the cross-sectio

1.	In order to maintain the desired shape of the tunnel, the cross-section of the tunnel must be checked at a regular interval of
A.	2 - 3 m
B.	4 - 5 m
C.	7 - 9 m
D.	10 - 12 m
Answer» B. 4 - 5 m