SOME ONE PLEASE HELP Determine the sum: (9r3s2t − 4r2s2t2 − 6rs2t3) + (−4r3s2t + 8rs2t3).

A. 3r10s10t10
B. −r3s2t + 4rs2t3
C. 5r6s4t2 − 4r2s2t2 + 2r2s4t6
D. 5r3s2t − 4r2s2t2 + 2rs2t3