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 .