  Aims. The aim of our study is to obtain the near-ultraviolet to visible
(NUV-VIS, 0.35 - 0.95 micron) reflectance spectra of primitive asteroids with a
focus on members of the Themis and Polana-Eulalia complex families. This
characterization allows us to discuss the origin of two recent sample return
mission target asteroids, (162173) Ryugu and (101955) Bennu. Methods. We obtain
low-resolution visible spectra of target asteroids down to 0.35 micron using
the telescopes located at the Roque de los Muchachos Observatory and revisit
spectroscopic data that have already been published. We study the
characteristics of the NUV-VIS reflectance spectra of primitive asteroids,
focusing on data of the Themis family and the Polana-Eulalia family complex.
Finally, we compare the NUV characteristics of these families with (162173)
Ryugu and (101955) Bennu. In this work, we also study systematic effects due to
the use of the five commonly used stars in Landolt's catalog as solar analogs
to obtain the asteroid reflectance in the NUV wavelength range. We compare the
spectra of five G-stars in Landolt's catalog with the spectrum of the
well-studied solar analog Hyades 64, also observed on the same nights. Results.
We find that many widely used Landolt's G-type stars are not solar analogs in
the NUV wavelength spectral region and thus are not suitable for obtaining the
reflectance spectra of asteroids. We also find that, even though the Themis
family and the Polana-Eulalia family complex show a similar blueness at visible
wavelengths, the NUV absorption of the Themis family is much deeper than that
of the Polana-Eulalia family complex. We did not find significant differences
between the New Polana and Eulalia families in terms of the NUV-VIS slope.
(162173) Ryugu's and (101955) Bennu's spectral characteristics in the NUV-VIS
overlap with those of the Polana-Eulalia family complex which implies that it.
