What is the difference between block ciphers and stream ciphers?

A Block ciphers are asymmetric; stream ciphers are symmetric B Block ciphers encrypt fixed-size chunks of data using modes of operation; stream ciphers encrypt data one bit or byte at a time by combining it with a keystream C Stream ciphers are slower but more secure than block ciphers D Block ciphers are used only for file storage; stream ciphers only for networks