A.after he had turned fifty
B.by the time he turns fifty
C.when he turned fifty
D.as soon as he turned fifty

A.I have been learning English for 10 years.
B.I learnt English for 10 years.
C.The last time I learnt English was 10 years ago.
D.I have started learning English for 10 years.

A.I have been learning English for 10 years.
B.I learnt English for 10 years.
C.The last time I learnt English was 10 years ago.
D.I have started learning English for 10 years.

A.Helen insisted on paying the money back to Linda.
B.Helen suggested paying the money back to Linda.
C.Helen promised to pay the money back to Linda.
D.Helen apologized to Linda for borrowing her money.

A.\(I = U\sqrt {{R^2} + {\omega ^2}L} .\)
B.\(I = \dfrac{U}{{R + \omega L}}.\)
C.\(I = \dfrac{U}{{\sqrt {{R^2} + {\omega ^2}{L^2}} }}.\)
D.\(I = \dfrac{{{U_0}}}{{\sqrt {{R^2} + {\omega ^2}{L^2}} }}.\)

A.\(\omega  = \dfrac{{{E_0}}}{{{\Phi _0}}}.\)
B.\(\omega  = {E_0}{\Phi _0}.\)
C.\(\omega  = \dfrac{{{\Phi _0}}}{{{E_0}}}.\)
D.\(\omega  = \dfrac{1}{{\sqrt {{\Phi _0}{E_0}} }}.\)

A.2,5cm.
B.5cm.
C.5mm.
D.0

A.\(90\,\,\Omega \).
B.\(150\,\,\Omega \).
C.\(250\,\,\Omega \).
D.\(1300\,\,\Omega \).

A.L, P, X.
B.L, P, Z.
C.M, P, Z.
D.N, Q, X.

A.0,66 m.
B.1,5 m.
C.6,6 m.
D.500 m.