No, quadrilateral ABCD is not a parallelogram.
To be a parallelogram, a quadrilateral must have two pairs of opposite sides that are parallel. However, in quadrilateral ABCD, only one pair of opposite sides is parallel:

Here is a Python code to calculate the slopes of the sides and check if the opposite sides are parallel:
import matplotlib.pyplot as plt
import numpy as np
# Define the coordinates of the quadrilateral
A = (2, 7)
B = (8, 1)
C = (1, -9)
D = (-6, -2)
# Calculate the slopes of the sides
AB_slope = (B[1] - A[1]) / (B[0] - A[0])
BC_slope = (C[1] - B[1]) / (C[0] - B[0])
CD_slope = (D[1] - C[1]) / (D[0] - C[0])
DA_slope = (A[1] - D[1]) / (A[0] - D[0])
# Check if the opposite sides are parallel
if AB_slope == CD_slope and BC_slope == DA_slope:
print("Yes, quadrilateral ABCD is a parallelogram.")
else:
print("No, quadrilateral ABCD is not a parallelogram.")
Output:
No, quadrilateral ABCD is not a parallelogram.
Therefore, the answer is (C).