What Hypothesis Were the Researchers Testing by Treating Tumors with Endostatin

What hypothesis were the researchers testing by treating tumors with endostatin and a standard chemotherapy drug?

A) Endostatin works on endothelial cells,and therefore natural selection for resistance will not occur in tumor cells.
B) Endostatin works on tumor cells,and therefore natural selection for resistance will not occur in endothelial cells.
C) The standard chemotherapy drug works on endothelial cells,and therefore natural selection for resistance will not occur in tumor cells.
D) The standard chemotherapy drug works on tumor cells,and therefore natural selection for resistance will not occur in endothelial cells.
E) No answer is correct.