Solution :
Here, we need to perform JOIN operation of the students and registration.
Use NATURAL JOIN operator 
and so no need to specify Join condition.
Also we need to selection operator tp select only those course whose major in "philosophy".
Finally we projection operator π to project only distinct students name who took at least three courses.
![$\pi [\sigma_{\text{student's nam}e} [ \sigma(\text{three courses}) \Join \text{"Philosophy"}]]$](https://tex.z-dn.net/?f=%24%5Cpi%20%5B%5Csigma_%7B%5Ctext%7Bstudent%27s%20nam%7De%7D%20%5B%20%5Csigma%28%5Ctext%7Bthree%20courses%7D%29%20%5CJoin%20%5Ctext%7B%22Philosophy%22%7D%5D%5D%24)
Answer:
Each of their sons has around a 0% chance for being color blind.
they will have normal girls but they will be carriers
Explanation:
Since the man is colour blind and he donates the X- Chromosome that is the carrier to the woman, they will give birth to a daughter who is a carrier but not color blind. If the man donates the Y chromosome, then they will give birth to a normal male child who is not color blind neither is he a carrier
Answer:
The cell address of 4th row and 4th column is
4D/D4
The SOA is the specific record type found in every zone and contains information that identifies the sever primarily responsible for the zone as well as some operational properties for the zone.
Explanation:
The Start of Authority Records (SOA) has the following information they are
Serial Number: This number is used to find when zonal information should be replicated.
Responsible person: The Email address of a person is responsible for managing the zone.
Refresh Interval: It specifies how often a secondary DNS server tries to renew its zone information.
Retry Interval: It specifies the amount of time a secondary server waits before retrying the zone information has failed.
Expires After: IT specifies the amount of time before a secondary server considers its zone data if it can't contact with the primary server.
Minimum TTL: It specifies the default TTL value for a zone data when a TTL is not supplied.
I believe a metal detector would be a fine choice for an employee entrance.
