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)
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Ziffcorp, an it firm, uses a technology that automatically updates the antivirus software in all the computers in the firm whenever the software becomes outdated. it is evident that Ziffcorp uses <span>push technology </span> for automatically updating the antivirus software. The push technology is I<span>nternet based communication system in which the transaction request is generated by the publisher or central web server.</span>
Answer:
d.) black-box testing
Explanation:
Software testing can be regarded as procedures/process engage in the verification of a system, it helps in detection of failure in the software, then after knowing the defect , then it can be corrected. Black Box Testing can be regarded as a type of software testing method whereby internal structure as well as design of the item under test is not known by one testing it. In this testing internal structure of code/ program is unknown when testing the software, it is very useful in checking functionality of a particular application. Some of the black box testing techniques commonly used are; Equivalence Partitioning, Cause effect graphing as well as Boundary value analysis. It should be noted that the purpose of black-box testing is to isolate the behavior of a given component of software.
