Electron-loss cross sections in Cq+(q=14)collisions with He,Ne,Ar are measured in the intermediate-velocity regime, and the ratio of the two-electron-loss cross section to the one-electrom-loss cross section, R21, are calculated. It is shown that a single-channel analysis is not sufficient to explain the results, and that projectile electron loss, electron capture by the projectile, and target ionization must be considered together to interpreter the data. The screening and antiscreening theory can annalyse the threshold velocity, but cannot totally explain the data of R21 with velocity increasing. The effective charge of target increases with velocity increasing. Ne and Ar have the same effective charges in the velocity regime, but He has a smaller one at the same velocity. The correlation between loss electrons is also analyzed.