Task: Question Answering
Input (English): Question: The specific test to be performed as a previous step to the insertion of a catheter in the radial or ulnar artery, in order to evaluate the presence of an adequate collateral circulation of the hand, is called: 
 Options:  <1> Spencer test modified. <2> Tolerance test for arterial catheterization. <3> Student's test <4> Allen test. <5> Tilt Test (TTT).
Output (English): 4