Being a devoted abolitionist until the end of his life made Thoreau’s life stimulating and compelling. Which of the following statements is not true about Thoreau as an abolitionist?

A、He wrote several essays, like "Slavery in Massachusetts" (1854) and “A Plea for Captain John Brown “(1859), to support abolitionist cause.;
B、He helped slaves escape to the North through the Underground Railroad.;
C、He moved into the political forefront only with his defense of John Brown.;
D、He wrote many books about how helpful and necessary slavery is.