【单选题】
下列图形中阴影部分构成的集合是凸集的是？
①
<img src=https://huaweicloudobs.ahjxjy.cn/7AF4876FB1B1766A53DFED1D3529B11B.png title=BPXU`$KY9[F$QS_TAXX7N%3.png alt=BPXU`$KY9[F$QS_TAXX7N%3.png/>
②
<img src=https://huaweicloudobs.ahjxjy.cn/A874DC9983A0A1F09A14E86AAC961C1B.png title=DD2Y$2D{_KWNSWC[VV]1S0G.png alt=DD2Y$2D{_KWNSWC[VV]1S0G.png/>
③
<img src=https://huaweicloudobs.ahjxjy.cn/A39CE71C1041F193EBEB035C5BA964E9.png title=}BZGG}[@_L_D7LD`EPZ_Q81.png alt=}BZGG}[@_L_D7LD`EPZ_Q81.png/>
④
<img src=https://huaweicloudobs.ahjxjy.cn/81AA82B6C6DFBBFCEF7A158B0ED99D99.png title=R%48HQEF_1PPMWOZ6YU$O(R.png alt=R%48HQEF_1PPMWOZ6YU$O(R.png/>