The correct answer is reciprocal cross.
The reciprocal cross is referred to a cross between a male of a specific strain with the female of another strain and the vice versa.
The reciprocal ensures that the inheritance of a certain character in the offspring in independent of the sex. This cross was done by Mendel, by switching the pure breeding lines.
Even after changing the sexes, he got the same results in F1 progeny, which suggest the inheritance of a character is independent of the sex.