Please help, marking brainliest for the correct answer

Ascientist wants to use a model to present the results of his detailed scientific investigation. why would a model be useful? a )because the model makes the concepts easier to understand b) because the model is easy to put together and to use c) because the model prevents other scientists from asking questions d) because the model requires the audience to pay full attention to it i don't know what to choose because between a and d a is much more likely than d because it only wants to get the attention of the audience. i'm confuse.

Which of the following pair(s) of circles have las a common external tangent? select all that apply. a and b a and c b and c

David leaves his house to go to school. he walks 200 meters west and 300 meters north. how far is david from his original starting point?