What is double substitution

In Tcl the words in a command are always exposed to two layers of interpretation: First, Tcl interprets them and prepares them as arguments to a routine. Second, the routine interprets those arguments according to its own principles. double substitution occurs when Tcl performs substitutions on original command and a routine then performs substitutions on the resulting arguments. Care is required in these cases to avoid errors, including vulnerability to injection attacks.

Explanation:

this probably wont help but here

the correct answer would be d. hope this !

most historians agree that gabriel mouton, the vicar of st. paul’s church in lyons, france, is the “founding father” of the metric system. he proposed a decimal system of measurement in 1670. mouton based it on the length of one minute of arc of a great circle of the earth (now called a nautical mile, 1852 meters). he also proposed the swing-length of a pendulum with a frequency of one beat per second as the unit of length (about 25 cm). a pendulum beating with this length would have been fairly easy to produce, thus facilitating the widespread distribution of uniform standards. over the years, his work was revised, improved, and extended by a number of french scientists.

the political sponsor of weights and measures reform in the french revolutionary national assembly was the bishop of autun, better known as talleyrand. under his auspices, the french academy appointed several committees to carry out the work of developing a usable system of weights and measures for france. one of the committees recommended a decimalized measurement system based upon a length equal to one ten-millionth of the length of a quadrant of the earth’s meridian (i.e., one ten-millionth of the distance between the equator and the north pole).