Question

Select the topic sentence.

1What is amnesia? 2Most of us think of a dramatic, total loss of memory brought on by a severe blow to the head. 3Amnesia is, however, a very subtle, and sometimes sinister, illness. 4While amnesia can result from a head injury, overwork and worry can also lead to memory lapses. 5In some cases, diagnosis is difficult because these lapses are intermittent, rather than constant.

Answer 1

The answer is 3: Amnesia is, however, a very subtle, and sometimes sinister, illness.

The reason for this is because that is the topic that the author is talking about: that Amnesia is a subtle and sinister illness.