Polarization phase curve of 1998 KU₂ along with those of three C-subgroup asteroids. Triple fitlines with the Lumme and Muinonen function (Eq. (7)) indicate F-types (dashed line and crosses), Ch- and Cgh-types (solid line and filled squares), and other C-types (dotted line and open triangles) with geometric albedo <0.1 (Zellner et al. 1974; Zellner & Gradie 1976; Belskaya et al. 1987, 2009b; Hadamcik et al. 2011; Gil-Hutton & Cañada-Assandri 2012; Nakayama et al. 2000, the unpublished data of Kiselev and Lupishko including the Asteroid Polarimetric Database (Lupishko 2014)).