判断题When we describe the sample used in a study, we commonly use the present tense(一般现在时态). However, when describing the general population from which the sample subjects were selected, the past tense(一般过去时) is normally used.单选题“The preplant treatments were sprayed on the surface of the prepared beds and they were incorporated into the soil by double-discing.” To shorten this sentence, which part can be omitted(省略)?