The answer is A. Air
because our sound travel in the air so bat`s waves should travel in the air to find the insects that are flying in the air! :)))
i hope this is helpful
have a nice day
We will all die because we need oxygen that the plants give is
A muscle fiber will respond to a stimulus when that stimulus reaches the threshold level. These local classified potentials which are mainly related with external stimuli extent the axon preliminary segment and construct up to they manage to extent the threshold value. The bigger the stimulus the larger the depolarization or try to reach threshold.