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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def resnet18(pretrained=False, **kwargs):
 """Constructs a ResNet-18 model. Args: pretrained (bool):
 If True, returns a model pre-trained on ImageNet """

    model = ResNet(BasicBlock, [2, 2, 2, 2], **kwargs)
    if pretrained:
        model.load_state_dict(model_zoo.load_url(model_urls['resnet18']))
    return model