Question: Of the following pairs of surface molecules, what is used by the virgin T lymphocytes to extravasate to the lymph node? 
 Options:  <1> CCR7 and L-selectin. <2> VCAM and L-selectin. <3> CCR7 and ICAM-1. <4> CCR9 and L-selectin. <5> CCR4 and VCAM-1.
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