1.- ¿Por qué será que los científicos de hace unos siglos no escogieron un patrón de medida por ejemplo un pedazo de varilla metálica para usarla como patrón de
medida y así ahorrarse miles de horas de mucho trabajo para encontrar una medida invariante del metro?

the word that best describes martin luther king jr.'s tone in the video is dignified

martin luther king, jr. was a social activist and baptist minister who played a key role in the american civil rights movement from the mid-1950s until his assassination in 1968. the video shows his manner and attitude having or showing a composed or serious manner that is worthy of respect so dignified is the correct answer

there are no contact forces mentioned on the list of choices that you've provided.

i think the answer is tomato juice? not entirely sure though