Reviewer 1: Ken Livingston

I really admire the work done in developing this detector and making this measurement.

Target of PRL is appropriate and part is very well written with clear exlpanations.
I don't have very many comments.

Page1
Paragraph 1.
The sentence ending " .. and scale Q^2." Is something missing there?

Page2 Bottom left para
Should probably have a reference to the CLAS detector here at the 1st point of it being mentioned.

Page2
1st paragraph in right hand column. "The RTPC ....."
I know it's a PRL, and there's not much room for more experimental detail, but I found it
difficlt from the text alone to get sense of how the BoNuS detector worked. 
A quick look at Figure 2.1 from the analysis note helped me enormously. 
I suggest including this, or a cut down version with the blow-up of the sense wires removed.  

It would be good to quantify both the timing resolution and the z resolution.

Page2. Right column, 2nd paragraph.
"Cuts on y< 0.8 ....." 
I don't think its clear what y is. It is a distance in mm? Or is a ratio whose definition I missed? 
In a short span of text there's mention of z,y,x where they all seem to be different physical 
quantities, which is a bit confusing. z a dimension, y = ?, x = x_b ?

Page 2 bottom right paragraph.
I assume that the plots in Figure 1 use the same events, 
but one makes use of the recoiling proton information and the other doesn't?
Perhaps that could be pointed out a bit more explicitly.

Is "neutron debris" a bit of standard terminology?

P3 1st paragraph
In discussion of the ratio you say
"... A_e nearly cancels..." 
and  later about radiative corrections 
"these also canceled to a large extent"
It would be better to aviod these rather subjective phrases and make a more quantitative statement.

When you state the rather well known value for Fn/Fd at x=0.3 can you include the value and error in brackets.
eg " ....value for Fn/Fd (=xxx.+/- yyy) at x=0.3." Not really to see the value, 
but to see the size of the error to back up the claim that it is well known.

Fig 3 caption. Space missing before "The arrow ..."




Reviewer 2: Stepan Stepanya

I read the draft and do not have any comments really.
The only question I have is the assignment of 3% error
on F^d_2 from the model fit. In the reference [20] it
says that the agreement with data and fit for F^d_2
is 3-5%. It can be seen from Fig.2 in [20] that the
agreement is Q2 dependent. I would suggest to
assign 5% systematic error for F^d_2, or at list they
should explain to us why 3%.

Stepan   



Reviewer 3:
Sébastien Procureur

I don’t have many comments as well on this paper; the work presented here is remarkable. 
I personally regret the lack of details: the outside reader has no way to check particular points of the analysis. 
I understand it is a PRL, and I would clearly support a future paper with more details on the analysis itself.

Concerning Fig. 1, I don’t understand the discrepancy appearing above 2.2 GeV, is it simply an acceptance effect? 
Maybe it could be commented somewhere, though it just serves as an illustration.

Also, I don’t like confusing statements like “the corrections due to the CLAS acceptance […] nearly cancels”, 
and a similar statement a few lines later (after Eq. 3). Could it be more quantitative?

Finally, I have some minor typos to report:

-          Abstract: “deep inelastic regions”, while in the rest of the paper “deep-inelastic” is used

-          The sentence starting with “The Bjorken scaling variable” after Eq. 1 has no verb

-          Same sentence: “where \nu is the the…”

-          2 lines below Eq. 4: “model independent”, while “model-(in)dependent” is used in the rest of the paper

-          Fig. 4: bottom left and right plots don’t have the same size