d.Integration testing.. because all other testing can 
performed once system/application is table and whole 
devlopment work over. But Integration testing we can do 
even if devlopment is in progress using stub or driver.

Let me know if you have any other thought

answer is integration testing actually the first three 
testing comes under performance testing i.e whether the 
system acepts multiple users' inputs with multiple 
transactions in that testing we are not bothered  much 
about the functionality rather performance of the system
but in integration testing we will look for field level 
validations and functionality of the module and emphasis is 
given to both of them

Its Integration testing
There are 2 types of requirements 1.Functional Requirements
2.Non-Functional Requirements
The load,stress and recovery are testing the performance of 
the application and fall under the Non-Functional 
Requirements testing
The Integration tesing is to insure that when the different 
modules are connected together there is correct data flow 
between the modules and all the modules are functioning 
correctly hence this falls under the functional requirements

its integration testing bcoz this is a level of testing 
while others are type of testing

Integration Testing is one type of White Box testing.While 
all others are black box testing.