Citation 3: The first sentence is "The sievert is a measure of radiation dose." It then states that the sievert is to gray, as rem is to rad.
Firstly, the gray is the measure of radiation dose. The sievert is a measure of the biological impact of an ionizing dose (i.e. a dose equivalent) so, in this context the first sentence is misleading because it's a better description of what the gray is. Secondly, if you think it is necessary to use this citation to explain to the audience what a sievert is, then the audience is unlikely to have any idea what gray, rem or rad are.
Finally, sievert is a unit, and gray is a unit. So sievert does not have the same units as gray.