multiple if conditions

Good day!
i have a table with 4 columns.
col1 col2 col3 col4
Please help me with a formula that outputs the following:
col1=empty & col2=empty & col3=empty & col4=empty => output a
col1>0 & col2=empty & col3=empty & col4=empty => output b
col1>0 & col2>0 & col3=empty & col4=empty => output c
col1>0 & col2>0 & col3>0 & col4=empty => output d
col1>0 & col2>0 & col3>0 & col4>0 => output e
i've tried all the if/and and if/or formulas but i don't find the solution.
Thanks in advance.
Have a nice day!