When I wrote of using a digital camera for recording freight cars, I was refering to the prototypes;
(I; wrote; of using a digital camera for recording freight cars) (I; was refering; to the prototypes; T:When I wrote of using a digital camera for recording freight cars)
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wrote was refering
of using a digital camera for recording freight cars
to the prototypes T:When I wrote of using a digital camera for recording freight cars