Употребите герундий в функции подлежащего.

1. It`s so uncomfortable to sleep on the floor.
2. It`s great to meet old friends.
3. It`s impolite to speak in a loud voice.
4. It`s always useful to think.

Я думаю, что тут скорее всего не герундий, а инфинитив надо в функции подлежащего, но приведу 2 примера с герундием и инфинитивом.

Герундий

1. Sleeping on the floor is so uncomfortable. 2. Meeting old friends is great. 3. Speaking in a loud voice is impolite . 4. Thinking is always useful .

Инфинитив

1. To sleep on the floor is so uncomfortable. 2. To meet old friends is great. 3. To speak in a loud voice is impolite . 4. To think is always useful .