【正确答案】 B

【答案解析】[解析] 题意：他们放弃了解救他们溺水朋友的希望。
划线词意为“放弃”。
A项end意为“结束”。例：The government acted to end a bakers" strike in the city. 政府采取行动结束了城里面包师傅的罢工。
B项abandon意为“放弃”。例：Fearing further attacks, most of the population had abandoned the city. 害怕城市进一步受到攻击，大多数人已经离开。
C项build意为“建立；加强”。例：Tension is building between the two nations. 两国之间的紧张关系正在上升。
D项strengthen意为“加强”。例：Our friendship has steadily strengthened over the years. 几年来我们的友谊有了持续的增进。故选B。