A.Suppose that the Internet connection hadn't been stable, the teacher could conduct the online lesson successfully.
B.Without the stable Internet connection, the teacher could conduct the online lesson successfully.
C.If the Internet connection had been unstable, the teacher could have conducted the online lesson successfully.
D.But for the unstable Internet connection, the teacher could have conducted the online lesson successfully.

A.Not until people are more concerned about online learning platforms has the COVID-19 resulted in schools shut all across the world.
B.Hardly had the Covid-19 result in schools shut all across the world when people are more concerned about online learning platforms.
C.Only after the COVID-19 has resulted in schools shut all across the world are people more concerned about online learning platforms.
D.Without people’s concern about online learning platforms, schools all across the world wouldn’t have been shut down.

A.\({q_1} > 0\) và \({q_2} < 0\)
B.\({q_1} < 0\) và \({q_2} > 0\)
C.\({q_1}.{q_2} > 0\)
D.\({q_1}{q_2} < 0\)

A.\({e_{tc}} =  - L\frac{{\Delta i}}{{\Delta t}}\)
B.\({e_{tc}} = 4\pi {.10^{ - 7}}{n^2}V\)
C.\({e_{tc}} = Li\)
D.\({e_{tc}} =  - L\frac{{\Delta t}}{{\Delta i}}\)

A.\(m\omega {A^2}.\)
B.\(\frac{1}{2}m\omega {A^2}.\)
C.\(m{\omega ^2}{A^2}.\)
D.\(\frac{1}{2}m{\omega ^2}{A^2}.\)

A.2 cm.
B.6 cm.
C.3 cm.
D.12 cm.

A.\(A = \sqrt {{A_1} + {A_2}} \)
B.\(A = \sqrt {\left| {{A_1} - {A_2}} \right|} \)
C.\(A = \left| {{A_1} - {A_2}} \right|\)
D.\(A = {A_1} + {A_2}\)

A.100 g.
B.1 kg.
C.250 g.
D.0,4 kg.

A.Chất rắn.
B.Chất lỏng.
C.Chất khí ở áp suất thấp.
D.Chất khí ở áp suất cao.

A.Tia Rơn-ghen có khả năng đâm xuyên.
B.Tia Rơn-ghen có tác dụng sinh lí.
C.Tia Rơn-ghen không có khản năng ion hóa không khí.
D.Tia Rơn-ghen tác dụng mạnh lên kính ảnh, làm phát quang một số chất.