Answer
a. There exists at least one dog which is not friendly.
b. There exists at least one person which is not happy.
c. No suspicions were substantiated/ All suspicions were unsubstantiated
d. No estimates were accurate/ All estimates were inaccurate
Work Step by Step
Negation of the statements of the form, " For all x, q", q being a statement is "There exists x, ~q" and vice versa.
