A、<span style="font-size: 16.8px; background-color: rgb(255, 255, 255);">E</span><span style="font-size: 12.6px; line-height: 0; position: relative; vertical-align: baseline; bottom: -0.25em; background-color: rgb(255, 255, 255);">a</span><span style="font-size: 16.8px; background-color: rgb(255, 255, 255);">＞U</span>
B、<span style="font-size: 16.8px; background-color: rgb(255, 255, 255);">E</span><span style="font-size: 12.6px; line-height: 0; position: relative; vertical-align: baseline; bottom: -0.25em; background-color: rgb(255, 255, 255);">a</span><span style="font-size: 16.8px; background-color: rgb(255, 255, 255);">＝0 </span>
C、<span style="font-size: 16.8px; background-color: rgb(255, 255, 255);">E</span><span style="font-size: 12.6px; line-height: 0; position: relative; vertical-align: baseline; bottom: -0.25em; background-color: rgb(255, 255, 255);">a</span><span style="font-size: 16.8px; background-color: rgb(255, 255, 255);">＜U</span>
D、<span style="font-size: 16.8px; background-color: rgb(255, 255, 255);">E</span><span style="font-size: 12.6px; line-height: 0; position: relative; vertical-align: baseline; bottom: -0.25em; background-color: rgb(255, 255, 255);">a</span><span style="font-size: 16.8px; background-color: rgb(255, 255, 255);">＝U</span>