V. Complete the sentences with the given words in their proper forms(用括号中所给的适当形式完成下列句子。每空格限填一词)(共6分) 49. How many capital ____have you learnt till (直到) now? (city) 50. Don’t speak ____in the English lesson. (China) 51. There are fourteen floors in the building and he lives on the ____floor. (twelve) 52. There is a tall ____behind our school. (build) 53. I ____go shopping with my mother on Sundays. (usual) 54. We are going to the ____next Friday. (exhibit)