H I line profiles from VLA-C, VLA-D, and FAST observations of IRAS 04296+2923 (left) and HI 0432+2926 (right). For IRAS 04296+2923, the H I emission lines were extracted from a circular region with a diameter of 3.4′, centered at RA = 04^h32^m48.9^s, Dec = +29° 29′53.1″. The H I absorption spectrum was obtained from a box region centered at RA = 04^h32^m48.6^s, Dec = +29° 29′57.4″, with a size of about 20″ × 20″. The black line represents the Nançay H I data from Chamaraux et al. (1995). For HI 0432+2926, the H I emission lines were extracted from a box region centered at RA = 04^h32^m33.7^s, Dec = +29° 26′26.5″, with a size of about 2.5′ × 4.1′. Because the angular resolution of the FAST telescope is relatively low, the two galaxies cannot be fully separated in the FAST H I image. Therefore, the FAST H I line profiles were extracted from two box regions, as indicated in Fig. A.1. In the left panel, the y axis of the H I absorption line is shown on the right, while those of the emission lines are on the left.