नीचे दो कथन दिए गए हैं: कथन (I) : समदैशिक (Isotropic) और समांगी... | Agrigyan

Precision Definitions in Levelling and Surveying:

• Statement (A) is Correct: A datum surface is any arbitrary or recognized reference level surface (such as Mean Sea Level) against which vertical elevations/reduced levels (RL) are calculated.
• Statement (B) is Correct: Line of collimation is defined as the imaginary optical ray intersecting cross-hairs and passing through the optical centre of the objective glass.
• Statement (C) is Incorrect: The first staff reading taken after an instrument setup is always the BACKSIGHT (BS), while foresight (FS) is the last reading taken prior to moving the instrument.
• Statement (D) is Correct: Height of Instrument ($HI = RL + BS$) represents the elevation of the plane of collimation above datum.
• Statement (E) is Incorrect: At a change point (CP / turning point), the two readings taken are a FORESIGHT from the preceding setup and a BACKSIGHT from the new setup, never an intermediate sight.

Interpretation of Contour Properties on Topographic Maps:

• Close contour lines match with (IV) Top of hill: Closely spaced contours denote steep slopes commonly encountered approaching a hill summit.
• Wider contour lines match with (I) Foot hill: Widely spaced contours represent gentle, flat terrain typical of valley floors and foothills.
• Depression matches with (II) Higher contour values outside: Closed concentric contour loops with elevations decreasing inward indicate a depression, pond, or crater.
• Crossing of ridge lines matches with (III) At right angles: Contour lines always cross ridge (watershed) lines and valley (thalweg) lines perpendicularly at $90^\circ$.

Rules for Selecting Survey Stations in Triangulation:

• Statement (A) is Correct: Minimizing the number of main survey lines reduces accumulated chaining and sighting errors.
• Statement (B) is Correct: The central base line is the backbone of chain surveying, running along the greatest length of flat open terrain in the center.
• Statement (C) is Incorrect: Offsets must always be kept as SHORT as practically feasible ($\lt 15\text{ m}$) because angular inaccuracies multiply rapidly with long offset distances.
• Statement (D) is Correct: Triangles should be well-conditioned (no internal angle less than $30^\circ$ or greater than $120^\circ$) to prevent geometric distortion during plotting.
• Statement (E) is Incorrect: The cardinal rule of surveying is to work from the WHOLE to the PART to isolate and prevent the accumulation of localized measurement errors.

Engineering Design Protocol for Bench Terracing:
In soil and water conservation engineering, the formal structural design of bench terraces focuses on three primary geometric parameters:

• Type of bench terrace: Selection between level/table-top bench (paddy), inward-sloping bench with drainage waterway (high rainfall steep slopes), or outward-sloping bench with shoulder bunds (low rainfall permeable soils).
• Terrace spacing: Vertical interval ($VI = \frac{S \cdot W}{100 - S}$) dictated by land slope ($S$) and soil depth.
• Terrace cross section: Determining cut-fill equilibrium balance, bench platform width ($W$), riser slope (typically $1:1$ for vegetative risers), and riser height ($D$).