What are the recommended measures for reinforcing planks in scaffolding according to NCh999?
a. Use wire or strap ties at the ends of the planks.
b. Join the planks end-to-end without leaving gaps.
c. Place a transverse piece of 100mm x 100mm under the platform in its central part.
d. Use longitudinal overlaps between platforms without intermediate uprights.
e. Place a transverse piece of 25mm x 100mm at the ends of the platforms that rest directly on the crossbars.

a) a, b, c, d, e
b) a, b, c, e
c) b, c, d, e
d) a, b, c, d