**Studying:**
Studying is an essential activity for students on a school day as it helps them acquire knowledge and understand the subjects they are learning. Through studying, students review and consolidate the information taught in class, complete assignments, and prepare for upcoming exams. It involves reading textbooks, taking notes, solving problems, and engaging in other learning activities.

**Playing:**
Playing is also a crucial part of a school day as it provides children with opportunities for physical exercise, social interaction, and relaxation. Playing allows students to release their energy, improve their motor skills, and enhance their overall well-being. It can involve various activities such as sports, outdoor games, board games, or creative play.

**Chatting with friends:**
Chatting with friends during school breaks or free time is a common way for students to socialize and maintain friendships. It allows them to share experiences, discuss common interests, and provide emotional support to one another. Engaging in conversations with friends can also help improve communication skills and build positive relationships.

**Wandering:**
Wandering, on the other hand, is not a productive activity on a school day. It refers to aimlessly roaming around without a specific purpose or destination. Wandering can lead to distractions, loss of focus, and wasted time. It is important for students to stay focused and engaged in meaningful activities during school hours to make the most of their learning opportunities.

In conclusion, the correct answer is options A, B, and C (Studying, Playing, and Chatting with friends). These activities contribute to a well-rounded school day where students have the chance to learn, socialize, and relax. Wandering, however, should be avoided as it does not contribute to productive use of time during school hours.