Concept: An abstract is a brief summary of a document. It helps users quickly understand the main content of a document without reading the full text.
Step 1: Understanding the purpose of abstract.
An abstract saves the time of the reader by summarizing the main points.
\[
\text{Abstract} \Rightarrow \text{Short summary of document}
\]
Step 2: Checking valid purposes.
Abstracts help in time saving.
They promote current awareness because users can quickly know about recent literature.
They also help in literature search because abstracts provide key information about documents.
\[
A,\ C,\ D \Rightarrow \text{Valid purposes of abstract}
\]
Step 3: Finding the incorrect purpose.
An abstract does not offer the full text. It only gives a summary. Full text means the complete document.
\[
\text{Abstract} \neq \text{Full text}
\]
Therefore, the correct answer is Offer Full-Text.