Digg Deep Inc. makes and leases a backhoe to Estes. Due to a defect attributable to Digg Deep's negligence, Estes is injured in an accident in which his neighbor Fortis is also hurt. In a product liability suit based on negligence, Digg Deep may be liable to​
a. ​Fortis only.
b. ​Estes only.c. ​Estes and Fortis.
d. ​no one.