Answer:
its the letter B 
Step-by-step explanation:
the meaning of ascertain means "find (something) out for certain; make sure of." , in the passage it gives you several answers to choose from.
A ) so light 
B ) look about 
C ) for the first time 
D ) to whom 
The reason why B is the correct answer is because if the meaning of ascertain is to "find (something) out for certain; make sure of." , the only option that is close to that definition is B.
Hope this helps !
UPDATE : for Edmentum users and maybe plato users it is B i just took the test and got it correct.