PAST PROGRESSIVE AND PAST SMPLE WITH "WHEN AND "WHLE Look at the pictures, then put the verbs in brackets into the correct form.

In October 1871, dry weather and an abundance of wooden buildings, streets and sidewalks made Chicago vulnerable to fire. ... Legend holds that the blaze started when the family's cow knocked over a lighted lantern; however, Catherine O'Leary denied this charge, and the true cause of the fire has never been determined.