A is fairly easy.
First weighing: Put 3 bottles in each pan. If one of these is heavier then it contains the heavy bottle, otherwise the remaining set of 3 does
Second weighing: From the set of 3 known to contain the heavy bottle. Put one bottle in the left pan and one in the right. If one of these is heavier then it is the required bottle, otherwise the third one is.
StuartR