Numpyのarrayの書き方について

質問内容

以下のコードでnp.argmax(ans[74,:])としているのですが，この",："と言うのはどう言う役割をしているのでしょうか？
なくても良いとどこかで見たのですが，そもそもこれが成している役割を理解していないので，そこを教えて頂きたいです．
初歩的な質問ですが，よろしくお願いいたします．

ソースコード

print(np.argmax(ans[74,:]))

ちなみにansについては以下のような配列になっています
[[ 1.038788 0.00653736 -0.05591957]
[ 1.0187379 0.02080166 -0.05594477]
[ 1.0370377 0.00731887 -0.05652656]
[ 0.98979425 0.05240192 -0.05683028]
[ 0.9245055 0.11933275 -0.05574812]
[ 1.0436664 0.00631815 -0.05559225]
[ 0.972157 0.07584003 -0.05698368]
[ 1.1543096 -0.11730845 -0.05134351]
[ 1.1142364 -0.07625021 -0.05291152]
[ 1.0114874 0.04723945 -0.0559618 ]
[ 0.94785094 0.11490752 -0.05836384]
[ 1.1232861 -0.1019475 -0.05575992]
[ 0.77998626 0.2947904 -0.06397741]
[ 0.9529484 0.10112719 -0.05674917]
[ 1.0405471 0.00570717 -0.0553266 ]
[ 0.8976544 0.16003689 -0.05855989]
[ 1.0501544 -0.00236954 -0.05721959]
[ 0.9527906 0.09947495 -0.05707815]
[ 1.0971435 -0.0551113 -0.05306423]
[ 0.97556424 0.06233923 -0.0556762 ]
[ 1.0651217 -0.0263672 -0.05475088]
[ 0.9912276 0.04603221 -0.05673647]
[ 0.8659526 0.20382865 -0.06172827]
[ 0.9886073 0.06567557 -0.05859347]
[ 1.0353901 0.01442273 -0.05614206]
[ 0.09894702 0.8172601 0.13452446]
[ 0.05939734 0.7117517 0.26539192]
[ 0.05252764 0.65304935 0.32328832]
[ 0.05394828 0.6656931 0.31049868]
[ 0.07681167 0.7432376 0.22050908]
[ 0.09343484 0.59957564 0.32709673]
[ 0.09336194 0.7153455 0.228075 ]
[ 0.17051113 0.76254386 0.11132681]
[ 0.01935339 0.52376235 0.46779224]
[ 0.00158271 0.4661367 0.5367465 ]
[-0.00746667 0.45134246 0.55815387]
[-0.02243468 0.41882724 0.6017381 ]
[ 0.10406119 0.77711165 0.16417101]
[ 0.0522007 0.68096393 0.2993314 ]
[ 0.03958595 0.595896 0.38536903]
[ 0.10033387 0.6841774 0.2475653 ]
[ 0.11930978 0.74595916 0.1756643 ]
[ 0.00561374 0.47303233 0.525437 ]
[ 0.07178396 0.7291198 0.23795915]
[ 0.08980915 0.70212674 0.24225679]
[ 0.01794466 0.51975054 0.4724503 ]
[ 0.09669209 0.7087347 0.23027965]
[ 0.05392921 0.6090232 0.35906163]
[ 0.07475829 0.6755165 0.28052944]
[ 0.25644016 0.70626444 0.07643156]
[-0.13286564 0.03327338 1.048471 ]
[-0.09049985 0.20593408 0.8555528 ]
[-0.11429569 0.1052635 0.9670434 ]
[-0.07194903 0.17449203 0.86320806]
[-0.1098865 0.12779549 0.94297194]
[-0.01984397 0.43012774 0.5895363 ]
[-0.06806871 0.27488258 0.7730558 ]
[-0.10687748 0.09220546 0.9711044 ]
[-0.06585845 0.28484243 0.7619575 ]
[-0.15106669 -0.00966451 1.1040138 ]
[-0.08303437 0.2243169 0.83210135]
[-0.12787494 0.07976314 1.0028336 ]
[-0.07567993 0.25290546 0.79970765]
[-0.01630181 0.4221871 0.59277725]
[-0.10791925 0.12357462 0.94469094]
[-0.09223327 0.20760904 0.85582495]
[-0.11247703 0.1051531 0.9653547 ]
[-0.09495208 0.17517601 0.8865198 ]
[-0.09853593 0.15441003 0.9083967 ]
[-0.01533192 0.42402795 0.5899646 ]
[-0.09525684 0.1713844 0.8904753 ]
[-0.08739874 0.17433576 0.879645 ]
[-0.09889624 0.16002503 0.9039998 ]
[-0.06221572 0.26912412 0.7721431 ]
[-0.07968774 0.21722339 0.83472526]]