There are two main reasons for this. There are two main reasons for this.

There arey are popular for two main reasons. They are popular for two main reasons.

First, houses in Japanese cities are smaller than those in other countries. First, houses in Japanese cities are smaller than those in other countries.

very good, many English native speakers wrongly omit "those in" haha

First,The first reason is because houses in Japanese cities are smaller than those in other countries. The first reason is because houses in Japanese cities are smaller than those in other countries.

Second, many landlords or building managers prohibit tenants from having medium-sized or large dogs, so they only allow small dogs. Second, many landlords or building managers prohibit tenants from having medium-sized or large dogs.

Second,The second reason is that many landlords or building managers prohibit tenants from having medium-sized or large dogs, so they-sized dogs and only allow small dogones. The second reason is that many landlords or building managers prohibit tenants from having medium or large-sized dogs and only allow small ones.

Popular dog breeds include Ttoy Ppoodles, Pomeranians, Cchihuahuas, and Shiba Inus. Popular dog breeds include toy poodles, Pomeranians, chihuahuas, and Shiba Inus.

you capitalize proper noun dog breeds (I had to look this up)

Popular dog breeds in Japan include: Toy Poodles, Pomeranians, Chihuahuas, and Shiba Inus. Popular dog breeds in Japan include: Toy Poodles, Pomeranians, Chihuahuas, and Shiba Inu.

Because "shiba inu" is a Japanese word/breed, you don't have to make it plural. 日本語の複数形と英語の複数形が違うので、日本語の言葉を英語で書いたら単数形のままでいいです。

I love dogs, but I can't have one because of the rules inat my apartment. I love dogs, but I can't have one because of the rules at my apartment.

So, I enjoy watching animal videos on YouTube or watching people walking their dogs in the park. So, I enjoy watching animal videos on YouTube or watching people walk their dogs in the park.

So, I enjoy watching animal videos on YouTube or watching people walking their dogs in the park. So, I enjoy watching animal videos on YouTube or watching people walk their dogs in the park.