why are experiments high on internal validity?

Question

A) the conditions can be replicated by other experimenters
B) they involve an independent as well as dependent variable
C) they involve numeric observations that can be statistically analysed
D) they are carried out inside laboratories

I am really confused between A and D.
I think it is A because the benefit of conducting a laboratory experiment is that conditions can be highly controlled. Everything apart from the Independent variable can be held constant so if changes in the independent variable are accompanied by changes in the dependent variable we can be fairly confident that it is the independent variable that caused changes in the dependent variable, rather than a confounding variable. So that means that experiments are high on internal validity

But Because they are conducted in such a controlled environment, they can be replicated. Outside the laboratory, on the other hand, it is much more difficult to create exactly the same conditions to replicate a study.

Can you please let me know the answer to this question if it is A or D please!!