I wrote these sentences:
"I think my work is so relevant to my application because teaching English language gave me a valuable opportunity to study English closely and to have a very solid understanding of its grammar, syntax, semantics , pragmatics, phonetics and etc, which I think is an essential foundation for anyone who wishes to tackle the field of translation and gain professional skills".
The problem is the word "is" ... Is it "is" because "essential foundation" is singular or should I use "are" because I am speaking about grammar, syntax, etc.?
I think "is" is right because I do speak about grammar, syntax and etc. as one thing or idea which is the "essential foundation".
I am not sure about this.