1) Легко ли делать фотографии? It is not easy do take pictures at all. This is a really hard work
2) Что интереснее - коллекционирование вещей или содержание домашних животных? In my opinion keeping pets is much more interesting because you have a lot of fun playing with them.
3) Что люди обязаны делать, когда у них есть домашнее животное? They must take care of it, feed and play with it. They also must take it to vet from time to time.
4) Какие вещи интересно или полезно собирать? In my opinion, it is both interesting and useful to collect coins because some of them are valuable and rare.