图示梁A截面弯矩影响线是( )。<img src=https://huaweicloudobs.ahjxjy.cn/9327DCBB933DC9F52AC8E0BC404D835F.png title=30.png alt=30.png/>
①
<img src=https://huaweicloudobs.ahjxjy.cn/D30A513889C86D71F61EE49EDED92E68.png title=31.png alt=31.png/>
②
<img src=https://huaweicloudobs.ahjxjy.cn/611D6A2F594855AD7B45EDEEA78DF805.png title=32.png alt=32.png/>
③
<img src=https://huaweicloudobs.ahjxjy.cn/901C5F6BF88A2D94A2FC5731DB6A6CC0.png title=33.png alt=33.png/>
④
<img src=https://huaweicloudobs.ahjxjy.cn/E110F1E7BD2E5A252A08B96BC8253E75.png title=34.png alt=34.png/>