Which sentence below would be the best topic sentence for the following paragraph? __________________________. They apply CNNs in two main ways. The first one is to learn the meaningful features and then apply classification methods to infer the pixel label. Representative methods include [AHG∗12,MYS14,FCNL13], but they are optimized to work for a lot of different classes, rather than focusing specifically on portraits. The second way is to directly learn a nonlinear model from the images to the label map. Long et al. [LSD14] introduce fully convolutional networks in which several well-known classification networks are “convolutionalized”.