On Earth, among the surest indications of sunspot cycles are believed to be the rate that trees grow, as seen in the rings visible in the cross sections of their trunks.

• AOn Earth, among the surest indications of sunspot cycles are believed to be the rate that trees grow  
• BOn Earth, among the surest indications of sunspot cycles are, it is believed, the rate of tree growth  
• COn Earth, the rate at which trees grow is believed to be among the surest indications of sunspot cycles  
• DAmong the surest indications on Earth of sunspot cycles, believed to be the tree growth rate  
• EAmong the surest indications on Earth of sunspot cycles is believed to be the rate at which trees grow