Which is the right way to concatenate two files in galaxy? It is option 1 or 2? Or it is the same?

Some times I can not do option 2, even in the same workflow, and I can not find why. Then, in the same work flow I have same files concatenated according to option one, and anthers according to option 2 and I do not know if it is a mistake.

Dr. Alejandro Colaneri

Departments of Biology

University of North Carolina at Chapel Hill

310 Coker Hall, CB# 3280

120 South Road

Chapel Hill, NC 27599-3280

Tel: 919-962-2273

fax: 919- 962-1625