“[ I ] should be concerned”

not “[me] should be concerned.”

[anyone] is used as the “subject”

so you use the “subject” form ” I ”

(b) Note: By itself,

you would say

“It is I” [not “it is me”].

“It’s me” or “It’s just me” is

commonly spoken colloquially,

but it is not grammatically correct.

“It is he” and

“This is she”

are also grammatically correct.

It’s like when someone calls, and you answer the phone, and they ask for you , and you say “this is she”.

My first impulse was to say “me”, but then I remembered that situation, which is why I picked I rather than me (because me would go with “this is her”. Same objective case, whereas I is nominative).

I always think if you turn the sentence around, you would say,

“it is I who should be concerned”.

Answers “who”, which is nominative case, as I recall.

I’m a little bothered to see so many teachers getting this wrong!

I’m not a teacher but I read, write and speak English…