Solution: Make auxiliary lines DE and EF to make BCEF rectangular.

Then S△CEF=(8+4)×4÷2=24cm2,

S squared ADEF=4×4= 16cm2,

Adf of sector s = 90 π×16360 = 4 π cm2,

∴ Shadow area = 24-( 16-4π) = 8+4π (cm2).

So choose: a.