A、] The mayor dwelt at the problem of traffic safety in his TV talk, in which he mentioned the deaths caused by traffic accidents had been on the rise since January. [
B、] The mayor dwelt on the problem of traffic safety in his TV talk, which he mentioned the deaths caused by traffic accidents had been on the rise since January. [
C、] The mayor dwelt in the problem of traffic safety in his TV talk, he mentioned the deaths caused by traffic accidents had been on the rise since January. [
D、] The mayor dwelt on the problem of traffic safety in his TV talk, in which he mentioned the deaths caused by traffic accidents had been on the rise since January.
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