Concatenate list of strings

I’m writing a Custom Node that will take as input a number in Decimal Feet and output it as Feet, Inches and Fraction.
I got everything to work, but then I decided I needed to make it accept a List of Decimal Feet instead of a single value.
Everything is working up until the very last node where I put it all together.
At first, I was using String.Concat which doesn’t like lists.
So I replace those with a simple Code Block str1+str2+str3+str4
The should return a list of 4 concatenated strings, but I’m getting 4 copies of the first value.
I don’t see anything wrong with this, but maybe I’m too close
Can anyone see my error?

Changed my Code Block to
str1<1>+str2<1>+str3<1>+str4<1>;
and it seems to work, but I really don’t understand why.
I thought I had it working the first time.
(OK, maybe it was the 12th time, but it did work once without the <1>)