Explanation:

Statement 1: Yes
All client computers in the Paris office will be joined to an Azure AD domain.
A virtual network named Paris-VNet that will contain two subnets named Subnet1 and Subnet2.
Microsoft Windows Server Active Directory domains, can resolve DNS names between virtual networks.
Automatic registration of virtual machines from a virtual network that's linked to a private zone with auto-registration enabled. Forward DNS resolution is supported across virtual networks that are linked to the private zone.
Statement 2: Yes
A virtual network named ClientResources-VNet that will contain one subnet named ClientSubnet You plan to create a private DNS zone named humongousinsurance.local and set the registration network to the ClientResources-VNet virtual network.
As this is a registration network so this will work.
Statement 3: No
Only VMs in the registration network, here the ClientResources-VNet, will be able to register hostname records. Since Subnet4 not connected to Client Resources Network thus not able to register its hostname with humongoinsurance.local Reference:
https://docs.microsoft.com/en-us/azure/dns/private-dns-overview
https://docs.microsoft.com/en-us/azure/virtual-network/virtual-networks-name-resolution-for-vms-and-role-insta