1. If the arguments have the same conclusions, but the premises in one argument contradict the premises in another argument, then these arguments cannot be used together. I am right?

2. For example I have two convincing arguments to justify belief in M:

I have two arguments to justify my belief in M. 

Argument A and argument B have the same conclusion, but the premises of argument A contradict the premises of argument B, so 

I cannot use them together at the same time because they would contradict each other. 

Can I use these two arguments separately when I need to? If I want to use argument A, I stop using argument B and start using argument A. 

If I want to use argument B, I stop using argument A and start using argument B. 

I want to know if I can do this or if I need to choose only one argument.

Will it be rational or not? Will there be any contradictions or not?