我正在检查输出sudo apt update
Hit:1 http://dl.google.com/linux/chrome/deb stable InRelease
Hit:2 http://packages.microsoft.com/repos/code stable InRelease
Ign:3 https://repo.mongodb.org/apt/ubuntu focal/mongodb-org/4.4 InRelease
Hit:4 https://repo.skype.com/deb stable InRelease
Hit:5 https://repo.mongodb.org/apt/ubuntu focal/mongodb-org/4.4 Release
Hit:6 http://archive.ubuntu.com/ubuntu focal InRelease
Get:7 http://archive.ubuntu.com/ubuntu focal-updates InRelease [114 kB]
Get:9 http://archive.ubuntu.com/ubuntu focal-backports InRelease [101 kB]
Get:10 http://archive.ubuntu.com/ubuntu focal-security InRelease [114 kB]
Get:11 http://archive.ubuntu.com/ubuntu focal-updates/main amd64 DEP-11 Metadata [283 kB]
Get:12 http://archive.ubuntu.com/ubuntu focal-updates/universe amd64 DEP-11 Metadata [355 kB]
Get:13 http://archive.ubuntu.com/ubuntu focal-updates/multiverse amd64 DEP-11 Metadata [944 B]
Get:14 http://archive.ubuntu.com/ubuntu focal-backports/universe amd64 DEP-11 Metadata [10,4 kB]
Get:15 http://archive.ubuntu.com/ubuntu focal-security/main amd64 DEP-11 Metadata [27,6 kB]
Get:16 http://archive.ubuntu.com/ubuntu focal-security/universe amd64 DEP-11 Metadata [61,0 kB]
Get:17 http://archive.ubuntu.com/ubuntu focal-security/multiverse amd64 DEP-11 Metadata [2.468 B]
Fetched 1.068 kB in 2s (507 kB/s)
Reading package lists... Done
Building dependency tree
Reading state information... Done
为什么第 8 行有一个空隙？
（Ubuntu 20.04.3。apt 的版本是apt/focal-updates,now 2.0.6 amd64）
/etc/apt/sources.list.d 文件夹的内容是
/etc/apt/sources.list.d$ ls
clipgrab-team-ubuntu-ppa-focal.list mongodb-org-4.2.list.save
clipgrab-team-ubuntu-ppa-focal.list.save mongodb-org-4.4.list
google-chrome.list mongodb-org-4.4.list.save
google-chrome.list.distUpgrade skype-stable.list
google-chrome.list.save skype-stable.list.save
graphics-drivers-ubuntu-ppa-eoan.list vscode.list
graphics-drivers-ubuntu-ppa-eoan.list.distUpgrade vscode.list.save
graphics-drivers-ubuntu-ppa-eoan.list.save yarn.list
libratbag-piper-ubuntu-piper-libratbag-git-focal.list yarn.list.distUpgrade
libratbag-piper-ubuntu-piper-libratbag-git-focal.list.save yarn.list.save
mongodb-org-4.2.list