Explanation #1: The Makshan thought that "we fix the roads" does not include removing thorns. "Tikun" connotes fixing mounds and cavities. Therefore, he asked (that "all needs of the Rabim" teaches removing thorns); We answered that all of these were explicitly taught, for they are included in "we fix..." (Therefore, "all needs of the Rabim" includes digging pits.) Explanation #2: The Makshan was not so fluent in the Mishnah. He did not know that it says "we fix the roads."

R. Chananel's opinion: We cited this verse, which was written regarding Ma'akeh (the Mitzvah to build a wall around a roof), for it is a Michshol (there is concern for injury). Inference: From the Mishnah with the Gemara, we can learn that one may not water land, except for what is Devar ha'Avud, lest the grain or trees planted in it get ruined. The same applies to other Avodas Karka. It is forbidden during Chol ha'Moed. Implied question: We say that one may water! Answer: This is only from an irrigation channel that passes through the field itself. It is not excessive exertion. One may fix pits and caves of an individual, and dig l'Chatchilah for a Rabim, since they need water. The Beraisa above says so, like I explained.

Explanation: [It is called only a hint] because the verse refers only to the future, but not to nowadays. However, he answered that we can learn from there.