While gas cells for earlier German zeppelins were made of goldbeater's skin (the outer membrane of cattle intestines) the cells aboard Hindenburg used a new material, similar to that used by the Americans, which was made by brushing layers of gelatine onto a sheet of cotton; this gelatine film was sandwiched between ...
I think its A. increase in the fern population size. For the answer.
C. Sonography
Sonography makes use of sound waves.
The answer your looking for is conduction.
