Tom asked me what was ( ) in the street when I came in.

Tom asked me what was ( ) in the street when I came in.

keeping on

taking on

carrying on

going on

本题考查的是常见动词短语的含义辨析。
keep on意为“反复做某事”；take on意为“显现、承担”；carry on意为“继续做某事”；going on意为“发生”。分析句意，“汤姆问我”、“在街上”，故D选项“发生”符合题意。
句意：汤姆问刚刚我进来的时候街上发生着什么。