Step 1: Work out how many girls enter Class I each year.
The question says 7,000 students enter Class I every year and boys are 45% of them, so girls are the remaining 55%. That gives \(7000 \times 0.55 = 3850\) girls entering in each of the nine years.
Step 2: Understand what "stayed on beyond elementary classes" means.
A girl who stays on beyond elementary classes is one who does not drop out by the elementary level, Classes I-VIII. If the elementary drop-out rate for girls in a year is \(g\) percent, the fraction who stay on is \((1-g/100)\), so the number of girls who stay on that year is \(3850 \times (1-g/100)\).
Step 3: Apply this to each of the nine years using the elementary girls' drop-out rates from the table.
1996-97 (\(g=59.5\)): \(3850 \times 0.405 = 1559\).
1997-98 (\(g=59.3\)): \(3850 \times 0.407 = 1567\).
1998-99 (\(g=59.2\)): \(3850 \times 0.408 = 1571\).
1999-2000 (\(g=58.0\)): \(3850 \times 0.420 = 1617\).
2000-01 (\(g=57.7\)): \(3850 \times 0.423 = 1629\).
2001-02 (\(g=56.9\)): \(3850 \times 0.431 = 1659\).
2002-03 (\(g=53.5\)): \(3850 \times 0.465 = 1790\).
2003-04 (\(g=52.9\)): \(3850 \times 0.471 = 1813\).
2004-05 (\(g=51.2\)): \(3850 \times 0.488 = 1879\).
Step 4: Add these nine values and divide by 9 for the average.
Adding them up gives
\[
1559+1567+1571+1617+1629+1659+1790+1813+1879 = 15084
\]
so the average is \(15084 \div 9 = 1676\), which is close to a whole number of about 1676.
Among the options, 1673 is the nearest whole number to this average, well ahead of 1475, 1573, and 1743, which are all too far from 1676 to be the intended match.
Final Answer:
The average number of girls who stayed on beyond elementary classes, from 1996-97 to 2004-05, is closest to 1673.
\[ \boxed{1673} \]