a membranous fold in a hollow organ or tubular structure, such as a blood vessel or the digestive tract, which maintains the flow of the contents in one direction by closing in response to any pressure from reverse flow. (找到对应单词之后,请将这段话的翻译也写上)
【简答题】A. Determine the total number of protons, neutrons, and electrons in one ammonia molecule. B. what is the total mass of protons, of neutrons, andof electrons in one ammonia molecule?
【单选题】指出下列句子中Gerundio的用法:Como todavía se desconocía la existencia del continente americano, sospechaban que, cruzando el océano Atlántico, se llegaría a los ricos imperios asiáticos como China y la India.