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Since then, Vanessa-Mae has made recordings;� (a)
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and
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Since then, Vanessa-Mae has been making�recordings;� (b)
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are both correct, depending on what the speaker wants to emphasize - the result/achievement/completeness of the action (a) or the process/duration of the ongoing action� (b).
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�but it was in 1994 that she entered the field of pop music. The album immediately became popular with pop and classical music fans.
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�became � is the best choice here, you have the past time indicator ( �in 1994 �) and you are narrating a past event, hence Past Simple ( �became �)
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That �s just my two pennies � worth; hope this helps.
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Giorgi�