【单选题】

After flexing its mechanical arm and finding some puzzling chemistry in a patch of Martian soil,the robotic rover Spirit began investigating the composition of a rock namedAdirondack yesterday with two science instruments and a microscopic camer

A、
Following programmed instructions from flight controllers, the six-wheel rover made several short turns and moved forward about six feet. It stopped within inches of the pyramid-shaped rock, about the size of a football. It was the vehicle’s second maneuver on the Martian surface since landing there on Jan. 3.
Scientists at the Jet Propulsion Laboratory in Pasadena,Calif., said they did not expect results of the first rock examination until early today.But they were already both pleased and puzzled over the soil test results.
"We’re starting to put together a picture of what the soil at Gusev is really like,"Dr. Steven W. Squyres ofCornell, the principal scientist of the mission, said at a news conference in Pasaden
A、He was referring to the Spirit’s landing site in Gusev crater, near the Martian equator. Two of the Spirit’s main science instruments, the M6ssbauer spectrometer and the alpha particle X-ray spectrometer, made a close examination of soil near the landing base.
German scientists in charge of the studies reported that X-rays emitted by the surface soil indicated a chemical composition mainly of silicon and iron, with smaller amounts of sulfur, chlorine and argon.Argon is a noble gas that is part of the Martian atmosphere. Previous Martian sites visited by landing craft also contained significant amounts of sulfur and chlorine.
Other members of the project’s science team said the M6ssbauer spectrometer found considerable amounts of the mineral olivine in the soil. Olivine, which contains oxygen, iron and magnesium, is often found in volcanic rocks. The Martian soil may resemble the volcanic soil of Hawaii.
"One possibility is that this soil is simply ground-up lava,"Dr. Squyres saiD、"That would surprise me, but it’s entirely possible that beneath .those grains there is solid rock and we are detecting some of that solid rock, not the s0il."
Another property of the soil perplexed geologists. The fine grains of the Gusev surface seem to stick together in dry clumps. Geologists suspected static electricity as the clinging force. If so, they said, the soil should collapse and flatten out when the M6ssbauer spectrometer pressed against the grounD、Nothing collapsed, leadingDr. Squyres to ask what force was. responsible for holding them together.
The last paragraph is mainly aimed at ______.
A、explaining the nature of the fine grains of the Gusev surface
B．discussing what force was responsible for holding them together
C．presenting the perplexion of the geologists on the existence of the static force on the Mars
D．introducing the main points of view on the static force on the Mars