A "sub genre" is essentially a classification of something within the genre it has already been classified in. For example hip hop might be a genre of music and a sub genre might be electronic hip hop. Electronic hip hop is another level of specificity to describe a musical genre, beyond the larger genre which is hip hop. This same method could be applied to many artistic concepts and classifications more generally.
I would say the answer is playing sadly with feeling. I don't believe that banging violently would produce a sound that makes the piano sound as though it "moans with melody" The other two answer choices wouldn't produce a sound like that either. So playing sadly with feeling seems to be the best choice.
Video is a newer version of film, whilst videos may be digital which makes them easily accesible. Film includes such things as film reels which might get damaged and like with vhs tapes, you must rewind them manually if you wish to watch it again. So basically, videos are more secure while films might be slightly tedious.
