Help me with my homework again pls and ty

Luis nervously answered the questions about how he had collected water samples in an empty plastic jugs and what he had concluded. He showed them the control groups , plain tap water and bottled water, and samples he took from a river, a pond and a drinking fountain. Luis explained how he used a water testing kit to test the waters purity and pointed at the results he had graphed.

The judges wanted to know how hiroko collected samples in different parts of the town. Hiroko told them that hiroko had put large circles of sticky paper on index cards and then tacked each card up where hiroko thought that there was a pollution from cars and factories. Hiroko also had to explain the chart hiroko made of hiroko's result.

not concrete, existing in thought or as an idea but not having a physical or concrete existence