It took a while to find the (sort of) obvious. I needed a Select statement that used the IF function and wanted the condition part to have an OR in it.
The standard syntax is:
if (condition, do this if true, do this if false)
if (questions.type='F', concat(a,b,c), concat(a,b,c,d,e) )
with an OR
if (questions.type='F'||questions.type='G', concat(a,b,c), concat(a,b,c,d,e) )