Why it is difficult for scientists to develop drugs that kill viruses

because viruses adapt and change over time. so by the time they come up with something that might help, the virus would most likely be different and harder for the vaccine to work

Explanation:

the correct answer is: d. the saltine and pretzel are made of flour, yeast, and baking soda, and salt. the pecan contains no flour but it does contain fats. the pecan is a nut that can be consumed as a healthy snack. first of all, pecans are a source of fat (monounsaturated fat), but they provide less fat than some other nuts. pecans are a rich source of dietary fiber, manganese magnesium, phosphorus, thiamin, vitamin e…