Ivan tried to call his great-grandmother Alena on her home telephone last Saturday, but there was no answer. When Alena came over for dinner on Monday, she asked Ivan why he never calls her. Ivan replied that he just tried to call her on Saturday. Alena remembered that she was out shopping most of the day Saturday and said that she has no way of knowing when she misses calls.

Ivan figures out a technological solution to this problem. He tells his great-grandmother that she needs...
A.
better phone reception.
B.
a long-life phone battery.
C.
a caller i.d. display.
D.
a louder phone ring.