He showed that flies did not grow from meat that was not exposed to air
chemicals that are secreted from antigen-presenting cells then activate helper T cells describes the role of cell-to-cell communication during a response to an invasion of antigens.
Explanation: Antibodies are present on the surface of the cells, and binds specifically to antigens and can also engulf pathogen and process these cells presenting them to MHC class 2. This complex is activated by helper T cells to secrete antibodies and macrophages. This interaction of B-cell and MHC class 2 complex with helper T cell is cell-mediated immune response.
The correct answer is C. The temperature of the water
Explanation:
In an experiment such as the one described about the speed of snails in water, the manipulated variable is the factor or element that is manipulated on purpose. This means the researcher or researchers slightly change this element to compare how this affects another variable. In this context, the manipulated variable is the temperature of the water because researchers used three different temperatures (cool, room-temperature, and warm), and therefore they manipulated or changed this factor. Moreover, it is expected temperature affects the distance nails move, which is the main variable.
