In 1990, the HST First Examined SN 1987A and Found

In 1990, the HST first examined SN 1987A and found a ring of glowing gas surrounding it. In 1994, HST found three rings of glowing gas. What happened during this interval?

A) The core of SN 1987A bounced not once but twice, producing two additional rings.
B) Radioactivity in the original ring heated it and caused it to expand and split.
C) The shock wave from SN 1987A triggered the formation of planetary nebulae in two nearby stars.
D) The optics on HST were repaired, resulting in better resolution.