下面哪个图是属于渐变构成（）？<br/> A、<img src="https://static.zxtiku.com/wangke/imgs/topic/551f1e3fbcb8aa42920870087049c089.jpg"/><br/> B、<img src="https://static.zxtiku.com/wangke/imgs/topic/f57b33e22d0848e0900743655ce44ca0.jpg"/><br/> C、<img src="https://static.zxtiku.com/wangke/imgs/topic/9d35b897f939a97aae57f8e4c4ce8a83.jpg"/><br/> D、<img src="https://static.zxtiku.com/wangke/imgs/topic/7d3038f89eb48310fda060c84cc444ee.jpg"/>