British colonial rule in the region of modern-day Malawi, where the revolt occurred, began between 1899 and 1900, when the British sought to increase their formal control over the territory to preempt encroachment by German or Portuguese colonial empires. The region became a British protectorate in 1891  and in 1907, was named Nyasaland. Unlike many other parts of Africa, where British rule was dependent on the support of local factions, in Nyasaland British control rested on military superiority. During the 1890s the colonial authorities put down numerous rebellions by the local Yao, Ngoni and Cewa peoples. British rule in Nyasaland radically altered the local indigenous power structures. The early colonial period saw some immigration and settlement by white colonists, who bought large swathes of territory from local chiefs, often for token payments in beads or guns. Most of the land acquired, particularly in the Shire Highlands, was converted into white-owned plantations where tea, coffee, cotton and tobacco were grown. The enforcement of colonial institutions, such as the Hut Tax, compelled many indigenous people to find paid work and the demand for labour created by the plantations, led to their becoming a major employer. Once employed on the plantations, black workers found that they were frequently beaten and subject to racial discrimination. Increasingly, the plantations were also forced to rely on a system of forced labour or corvée, known locally at the thangata.
Question: How many major crops were grown on white owned plantations?
Answer: 4