Which one of the following statements is not correct with regard to heading and hench-ing method of tunnelling.

• A. Driving of tunnel is done in two portions of its section
• B. Driving the top portion is done in advance of the bottom portion.
• C. After driving the top portion 3 m to 3.5 m holes are drilled into the head and bench.
• D. Firing of head holes is done just before the bench holes are fired.