What Hypothesis Were the Researchers Testing by Treating Tumors with Endostatin

What hypothesis were the researchers testing by treating tumors with endostatin and cyclophosphamide?

A) Because endostatin works on endothelial cells, natural selection for resistance will not occur in tumor cells
B) Because endostatin works on tumor cells, natural selection for resistance will not occur in endothelial cells
C) Because cyclophosphamide works on endothelial cells, natural selection for resistance will not occur in tumor cells
D) Because cyclophosphamide works on tumor cells, natural selection for resistance will not occur in endothelial cells