Question: Of the following surface markers, one of them is expressed only in the virgin T lymphocytes, while the rest are also found in the population of activated T lymphocytes. Which? 
 Options:  <1> The adhesion molecule L-selectin. <2> The T lymphocyte receptor (TCR). <3> The integrin LFA-1. <4> The CD4 co-receptor molecule. <5> The integrin VLA-4.
1