Nhận biết (M1)

With some elements, like phosphorus, scientists were able to isolate a relatively pure sample of the

substance shortly after discovering its existence—but this wasn’t the case with all elements. ______ the

isolation process took a few years. The element molybdenum, for instance, was discovered in 1778 but

not isolated until 1781.

Which choice completes the text with the most logical transition?

• A.

  Even so,

• B.

  Often,

• C.

  Specifically,

• D.

  In fact,