Grammar should be taught by:

The correct option is "Enabling practice in context".

Step-by-Step Explanation:

1. Understanding the Goal of Grammar Teaching:
The primary goal of teaching grammar is to enable learners to use the language effectively, accurately, and naturally in real-life communication. Grammar is not just a set of isolated rules but a tool for creating and understanding meaning.

2. Analyzing the Options:
• "Making learners do written assignments": While written assignments are helpful, doing them mechanically without context often leads to rote learning where learners cannot apply the rules when speaking or writing freely.
• "Encouraging students to memorize rules": Memorizing abstract grammatical rules (deductive learning) does not guarantee communicative competence. Students might know the rule but fail to use it correctly in conversation.
• "Giving adequate assignments to learners": Similar to written assignments, quantity of homework does not ensure a deep conceptual understanding or practical usability of grammar.
• "Enabling practice in context": Learning grammar in context (inductive learning) means presenting grammatical structures through meaningful situations, dialogues, or texts. This allows learners to see how grammar functions in real communication, helping them internalize the rules naturally and apply them accurately in their own language production.

3. Conclusion:
Teaching grammar through contextualized practice is widely recognized by modern language pedagogy as the most effective method because it bridges the gap between knowing a rule and being able to use it dynamically in real life.