I have _____ books on my desk.
a lot of 意为“许多”，用来修饰复数可数名词或不可数名词，故答案为选项D。
There _____ an art room,a dining hall and ten classrooms in this school.
本题考查 there be 句型的就近原则。先根据 there be 句型的结构排除选项D；主语是 an art room，a dining hall and ten classrooms，根据就近原则可知，be 动词要和离它最近的主语部分即 an art room 保持一致，故答案为选项B。
— _____ students are there in your class?
— There are forty students.
答语的含义是“有40名学生”，由此可知，问句的含义是“你们班有多少名学生？”，how many 意为“多少”，对可数名词的量进行提问，故答案为选项A。