Here are the answers for each question:

**Question 21:** Lan should install this __________ on her smartphone. It helps to make her photos more beautiful.
**Answer:** **B. software**

**Question 22:** If you have an __________, you don't have to bring all those heavy books in your bag.
**Answer:** **B. e-book reader**

**Question 23:** I think this is a __________ problem. The computer screen is broken.
**Answer:** **C. device**

**Question 24:** Washing machine or vacuum cleaner can help you to __________ time while doing housework.
**Answer:** **B. save**

**Question 25:** A robot vacuum cleaner is a __________ device in your home. It makes housework less tiring.
**Answer:** **C. helpful**