The first activity is a crossword game. The words in rows and columns of the crossword which one student faces are randomly given by the server system and different from the words which another student faces. After the student fills in the rows and columns and clicks the button “Check crossword”, the server will check the correctness of the answers and give a grade. Considering the smaller screen of smart phones, we limit both the maximum rows and columns to ten words so that the students need not to drag the screen up and down many times to view the whole crossword matrix.