Vocab prob

we are not sure whether the tickets we got for the concert are still available. Nonetheless, we decided to go ___ with our plan and tried every ticket counter. (off, forth, through, further)

the radiologist had to perform ___ MRI on Steve as other imaging methods such as x-ray and CT scan have not been able to assess adequately the presence of certain diseases in his ailing body. (an, -, a, the)