Which statement describes the best procedure to determine if a vaccine for a disease in a certain bird species is effective?
(a) vaccinate 100 birds and expose all 100 to the disease.
(b) vaccinate 100 birds and expose only 50 of them to the disease.
(c) vaccinate 50 birds, do not vaccinate 50 other birds, and expose all 100 to the disease.
(d) vaccinate 50 birds, do not vaccinate 50 other birds, and expose only the vaccinated birds to the disease.

Grilled ham and cheese sandwich: caution: if you’re underaged then have a responsible adult supervising you to prevent any injuries.1. preheat a pan or griddle over medium heat. spread each bread slice with mustard — crust to crust is a must to get full coverage so that each bite is identical. if you don’t like mustard then use whatever else you like.2. use a trio of cheeses in a grilled cheese to achieve perfect harmony: 1 slice of american cheese for gooeyness, 1 slice of aged cheddar for sharpness and 1 slice of provolone or mozzarella for stringiness. if you don’t like these cheeses then use whatever else you like.3. ribbon your meat onto your sandwich to create dramatic height and a smoother bite down. don't just lay the meat flat — it makes for a flat sandwich.4. add anything else you'd like to the sandwich — (just make sure you season them with a bit of salt and 5. spread mayo on the outside of a grilled cheese before it goes into the pan or onto the griddle, which ensures that it will be perfectly golden brown every time.6. place on the griddle; dome your grilled cheese with a metal bowl to create a vortex of heat and ensure the cheese melts without over-toasting the exterior for a maximum of 3 minutes. flip, cover again and cook until the cheese is melted and the sandwiches are golden brown for a maximum of 3 minutes. hope this : )

Ibelieve this would be an obstacle.

Is this used on a test? ?