1. (2004 College Entrance Examination, Chongqing Paper) In a speech contest held by a senior high school grade, there are 10 students participating, including 3 from Class 1, 2 from Class 2, and 5 from other classes. If the order of their speeches is determined by drawing lots, then the probability that the 3 students from Class 1 are exactly grouped together (meaning their speaking order numbers are consecutive), while the 2 students from Class 2 are not grouped together is ( )
A. $\frac{1}{10}$
B. $\frac{1}{20}$
C. $\frac{1}{40}$
D. $\frac{1}{120}$
1. B $P=\frac{6!\times 3!\times 7 \times 6}{10!}=\frac{1}{20}$