Although Parliament repealed the townshend duties, why did they retain the tax on tea?

In 1770 most of the Townshend taxes were repealed, but taxes on tea were retained. ... Colonists would willingly pay for cheaper Company tea, on which the Townshend tax was still collected, thus legitimizing Parliament's ability to tax the colonies.

a historian researching the immigration policies of the early 1900s would expect a source written today,rather than in 1910 to :

( a ) be more interested in objective data and statistics.