a) AIA 171 Å image at 15:30:11 UT. The AR 12158 is enclosed by the white dashed box. b) AIA 94 Å image at 15:30:01 UT, which features an MFR pointed out by the white arrow. A vertical slice S1 (white solid line) is used to investigate the slow rise and expansion of the coronal loops. c) HMI LOS magnetogram at 15:30:35 UT. The contours (±400, ±800, and ±1200 G) of the LOS positive and negative magnetic field are overlaid on the 171 Å image with blue and green lines, respectively.