矩形线圈abcd，长ab=20cm，宽bc=10cm，匝数n=200，线圈回路总电阻R=5Ω．整个线圈平面内均有垂直于线框平面的匀强磁场穿过，若匀强磁场的磁感应强度B随时间t的变化规律如图所示，则：

区域要实现可持续发展，必须充分利用有利的自然条件，同时对不利的地理条件进行合理改造，这样才能因地制宜发展经济。下列对自然条件的利用或改造符合可持续发展原则的是（   ）

阅读下文，回答问题。
                                                                                             七子之歌(节选)
                                                                                                    澳门
                                                                                    你可知“妈港”不是我的真名姓?……
                                                                                    我离开你的襁褓太久了，母亲!
                                                                                    但是他们掳去的是我的肉体，
                                                                                    你依然保管着我
                                                                                    内心的灵魂。
                                                                                    三百年来梦寐不忘的生母啊!
                                                                                    请叫儿的乳名，叫我一声澳门！
                                                                                    母亲!我要回来，母亲!
                                                                                                    香港
                                                                                    我好比凤阁阶前守夜的黄豹，
                                                                                    母亲呀，我身份虽微，地位险要。
                                                                                    如今狞恶的海狮扑在我身上，
                                                                                    啖着我的骨肉，嗳着我的脂膏；
                                                                                    母亲呀，我哭泣号啕，呼你不应。
                                                                                    母亲呀，快让我躲入你的怀抱!
                                                                                    母亲!我要回来，母亲!
                                                                                                     台湾
                                                                                    我们是东海捧出的珍珠一串，
                                                                                    琉球是我的群弟我就是台湾。
                                                                                    我胸中还氲氤着郑氏的英魂，
                                                                                    精忠的赤血点染了我的家传。
                                                                                    母亲，酷炎的夏日要晒死我了；
                                                                                    赐我个号令，我还能背城一战。
                                                                                    母亲!我要回来，母亲!
       (注：“七子”：即被帝国主义国家霸占或“租借”的七个地区：澳门、香港、台湾、威海卫、州湾、九龙、旅顺大连；“妈港”：澳门的葡语音译；“郑氏”：收复台湾的民族英雄郑成功。)