Here we are getting more into details of what constitute a "good" channel. Strategy question, requires you do some evaluating and ... thinking (ouch!) If you didn't get here immediately, you may have misread the question.

2.    Choosing an indirect channel probably will be better than a direct channel if a producer wants to:

    a)    obtain a very aggressive selling effort.
        Well, maybe yes, but most likely not. In fact, chances are higher that an aggressive sales effort be better done through a direct channel, where salespeople of the firm itself promote the products.
    b)    adjust large discrepancies of quantity and assortment.
        Indeed, this seems more like it: when you use an indirect channel, i.e. middlemen, discrepancies are more easily adjusted, since they are part of the function of middlemen.

    c)    be more sensitive to coming changes in customer needs and attitudes.
        Nope, this is of course the opposite: direct channels will give the company more and faster information on what is happening in the channel.

    d)    provide special technical service.
        Same as above: direct channels are more efficient at providing special technical service to their customers.

    e)    make it easier to do marketing research.
        Similar to answer c): direct channels means being closer to customers and therefore in a better position to do market research.