What note letter does the 3rd or middle line start at for the: -Treble Clef
-Alto Clef
-Bass Clef

For Treble Clef, it is B. For Bass Clef, it is D. For Alto Clef, it is C.

Explanation:

We are given three different clefs and we must find the note of 3rd or middle line of each. First, we can start with Treble Clef, because most people begin to read that clef before the others.

In Treble Clef, we have to find the 3rd line. So we can remember it by:

Every Good Boy Deserves Fudge

Since "Boy" is representing the 3rd line, we can conclude that B is the 3rd line.

Now, for the rest, we just have to move it down according to clef.

For Bass Clef, remember that it is for lower instruments, so remember that lines are +2 higher than treble clef. So, up two notes from B is D.

While for Alto Clef, move it down one line so that it is a C.