He doesn't know their addresses.

He doesn't have enough paper.

He can't remember all their names.

It's taking too long to contact each one individually.

Building a prototype immediately.

Asking friends for help.

Understanding the problem thoroughly.

Buying the necessary materials.

A colorful banner.

A sound signal.

A written message.

A larger flag.

A type of engineering material.

A tool for measuring distances.

An early version to test ideas.

A final version of a design.

By flashing lights.

By playing a song.

By sending a text message.

By raising a flag.

By testing and making improvements.

By ignoring feedback.

By copying other designs.

By making them more expensive.

Cooking and cleaning skills.

Critical thinking and creativity.

Mathematics and history knowledge.

Sports and physical fitness.