Mark the letter A, B, C, or D on your answer sheet to indicate the correct answer to each of the following questions.

Lessons from the _____ developed countries are worth learning to save our time.

A. economically

B. economic

C. economize

D. economical

Cho các chất: HNO₃, KOH, Ag₂SO₄, NaCl, H₂SO₃, CuSO₄, Cu(OH)₂. Các chất điện li mạnh là

A. KOH, Ag₂SO₄, NaCl, H₂SO₃

B. NaCl, H₂SO₃, CuSO₄

C. HNO₃, KOH, NaCl, CuSO₄

D. Ag₂SO₄, NaCl, CuSO₄, Cu(OH)₂