Preparation

An informal letter usually starts with a casual and informal greeting, such as "Hi!", "Dear (Name of the recipient)", etc. The greeting is followed by a casual and personal touch. This can include asking about the recipient's well-being or briefly wishing them well. Unlike the formal letters, there is no set structure of the letter's body.

An informal letter is a personal letter written to your near and dears. The tone of the letter is casual, conversational, and informal. Informal letters are usually written to one's family, close friends, acquantainces, etc. 

Find below ten examples of articles:

1. I saw a cat in the balcony.
2. She wants to buy a house.
3. Can I have a bottle of juice, please?
4. He is an engineering at some big tech firm.
5. We had an antique vase in our living room.
6. I had an icecream for dinner.
7. The sun rises in the east.
8. She went to the store by the ocean.
9. The weather is gloomy today.
10. She was a quiet girl, sitting under an umbrella by the beach.

In English grammar, articles are words to come before a noun and indicate whether the noun is specific or general. The definite article (the) is used while talking about a specific noun. Whereas, indefinite articles (a, an) are used for general nouns or a noun whose indentity remains unknown.

For such kinds of sentences, Who will be converted to Whom and vice versa for making active to passive voice. Here, you is the subject and whom is the object.

Hence, the correct answer will be "Who has been called by you?" 

Passive voice is a type of sentence in which the subject receives the action instead of becoming the doer. Here, the focus will be on the object, and there will be a little focus on the subject or doer. I.e. A mango was eaten by Ram. In this sentence, the emphasis is on Mango instead of Ram. 

The passive voice writing style is suitable for formal writing, scientific reports or any such situation where the subject is less important than the object, like the experiment was conducted. It highlights the action or result. In such style of writing object is doer instead of subject.

In normal English it is advised to write sentences in active voice only. Since the sentence structure of active voice is simple and easy to understand for a user, unless asked, we need to prioritize writing in active voice only. It is generally preferred for straightforward communication or in Technical writing.