下面哪些选项是符合下面中心句的例子？
中心句：Despite the proliferation of mobile phones and computers in society, there are still situations in which written letters are a preferable choice of communication.
A、For instance, it is easy to see that many things are changing in the world.
B、Signed thank-you cards or new year cards show one's thoughtfulness to others.
C、love letters are highly appreciated when the partner takes the time to write them.
D、in business, electronic  letters are very convenient.