A bird sanctuary used to receive 10,000 birds per year. The number of birds migrating to the sanctuary is decreasing at the rate of 5% each year. Identify the exponential decay function that models the situation. Then find the bird population after 4 years.

a- y = 10000(0.5); 7800
b- y = 10000(0.95)t ; 8000
c- y = 10000(0.9)t ; 7900
d- y = 10000(0.95)t ; 8145