Lookup Column Header based on cell value

Hi,

Hoping to tap into your collective experience to help me with this! I have a spreadsheet an excerpt of which is as follows:

K L M N
1 Doors Security Vehicle Key
2 TRUE FALSE FALSE FALSE
3 FALSE TRUE TRUE FALSE
4 FALSE FALSE FALSE FALSE

Want I want to happen is to return the column header where there for a cell which contains "TRUE" in a blank column. If there isn't a cell with the value "TRUE" then to return "N/A". In the above example in blank column P for Row 2 would be "Doors", Row 3 would be "Security,Vehicle" and Row 4 would be "N/A".

In my actual spreadsheet I have 12 columns (L to W) which have the TRUE or FALSE values.

I know it has something to do with either HLOOKUP, INDEX and MATCH but can't seem to get it right. Any ideas?