Answer:
C. The Wallaces thought the Packard was driven by Mr. Granger.
Step-by-step explanation:
Since Mr. Granger has the same car as Uncl Hammer, The Wallaces thought that he was Mr. Granger. Due to their accusations they slowed down their car and waited for Uncle Hammer aka "Mr. Granger" to pass. This is how Uncle Hammer manged to drive across the bridge before the Wallace men did.