题目内容：

    It can be tough to pull kids away from their computers and mobile devices these days. While they're playing games, wouldn't it be great if they could be learning at the same time? Good educational apps offer fun challenges that teach specific grade-level skills. Here are 4 that combine fun and learning.

Understanding Math---Addition and Subtraction ($3.99; iOS)

Understanding Math---Addition and Subtraction goes beyond basic comprehension to instill a deeper understanding of the whys and hows of math. The app tracks your child's progress to determine strengths and weaknesses in different skill areas, and you can customize your child's learning experience to suit the needs.

Word Creativity Kit ($52.99; iOS)

Word Creativity Kit aims to make creative writing fun while also build up grammar rules. The app presents a series of words from seven categories, such as space or fantasy. Kids add their own words to finish the complete thoughts that these words have inspired.

Barefoot World Atlas ($4.99; iOS)

Barefoot World Atlas helps kids learn about geography and world cultures with a touch of the screen. Each region features a set of subtopics, from wildlife and natural features to native people, landmarks, and architecture. These facts and illustrations are delivered in photographs, sounds, and hundreds of mini videos.

My Grades & Homework (S0.99; iOS)

A combination of grades and homework tracker, My Grades & Homework can help your child stay organized and on top of the progress in school. A convenient calendar and course list format offer a glance at your child's assignment schedule that he/she might not normally get from standard homework planners.

1.What is the common part of the four apps?

A.They can encourage children to study harder.

B.They cam help parents know their children's progress.

C.They can make study fun by mini videos.

D.They can be installed into iOS operation systems

2.What is the purpose of the text?

A.To encourage parents to allow their students to play apps.

B.To wish readers to bring in more similar apps for children.

C.To introduce 4 educational apps for readers to buy and use.

D.To design the educational apps to combine fun and learning.