Ascospores from a Cross A $\times$ B C (All Auxotrophic Markers)are Analyzed

Multiple Choice

Ascospores from a cross a $\times$ b c (all auxotrophic markers) are analyzed.If genes b and c are linked,10 map units apart,but gene a is located on a different chromosome,what proportion of ascospores is expected to be a⁺b⁺c⁺?

A) about 12.5%
B) about 22.5%
C) about 25%
D) about 45%
E) about 50%