Take Care:
To finish an informal letter, the correct option is 'A' - Take Care. This phrase is commonly used to express well wishes and concern for the recipient's well-being. It is a thoughtful way to conclude a letter, showing that the sender cares about the recipient's welfare.

Explanation:
When writing an informal letter, it is important to end it in a friendly and warm manner. The phrase "Take Care" is a common and appropriate way to do so. Here's why it is the correct answer:

1. Expressing concern:
By using the phrase "Take Care," the sender is conveying their concern for the recipient's well-being. It signifies that the sender wants the recipient to stay safe, healthy, and happy. It shows a level of care and thoughtfulness towards the recipient.

2. Warm and friendly tone:
"Take Care" is a friendly and warm way to end a letter. It adds a personal touch to the communication and creates a positive impression. It helps maintain a friendly tone throughout the letter and leaves the recipient with a sense of goodwill.

3. Politeness and courtesy:
Adding "Take Care" at the end of a letter is a polite and courteous gesture. It shows that the sender acknowledges the recipient's presence and values their relationship. It is a simple way to express gratitude and show respect towards the recipient.

4. Commonly used closing:
"Take Care" is a widely accepted and commonly used closing phrase in informal letters. It is familiar and understood by most people, making it a safe and appropriate choice. It is a traditional way to conclude a letter and is considered socially acceptable.

Conclusion:
In conclusion, the correct option to finish an informal letter is 'A' - Take Care. This phrase demonstrates concern, maintains a friendly tone, reflects politeness, and is a commonly used closing. It is a thoughtful way to end the letter and leaves a positive impression on the recipient.