A. Te=(T1/2+T÷(T1/2·T B. Te=(T1/2·T÷(T1/2+T C. Tb=(T1/2+T÷(T1/2-T D. Tb=(T1/2·T÷(T1/2+T E. Te=(T1/2-T÷(T1/2·T
A. 2 B. 3 C. 4 D. 5