题目3单选题
图中为一平面简谐波在 t = 2 s 时刻的波形图,则P处质点的振动方程是 <img src="https://tihai-oss-cloud.itihey.com/img/68137e41b2646a3429cbab74a357f5dd.png">A. <img src="https://tihai-oss-cloud.itihey.com/img/ebed9ada8ea9c14825184c4337c283ae.png">B. <img src="https://tihai-oss-cloud.itihey.com/img/5f03ca397f498526cb63dd978a75de53.png">C. <img src="https://tihai-oss-cloud.itihey.com/img/852190480f8217201f972a0291ee27a6.png">D. <img src="https://tihai-oss-cloud.itihey.com/img/23b358fb8a84a8cf4af04b95313ecaf1.png">