Please list a patient's platelet level if it is within the normal range and if he or she is diagnosed with MCTD.
PLT > 100 and PLT < 400 means platelet level is within the normal range; PLT < 100 and PLT > 400 means platelet level is not within the normal range; diagnosed with MCTD refers to Diagnosis = 'MCTD';
SELECT T2.PLT FROM Patient AS T1 INNER JOIN Laboratory AS T2 ON T1.ID = T2.ID WHERE T1.Diagnosis = 'MCTD' AND T2.PLT BETWEEN 100 AND 400